Repair Information For Your Imperial's Spark Plugs


Imperial Home Page -> Repair -> Electrical System ->Ignition System ->Spark Plugs

Tips from Ross:


 Stay with the top names . . you can't ever go wrong with Champions. Note that a VERY specific plug was indicated, and contact them with questions for specific applications. These will include: nonleaded gasoline with retarded timing, different carburetor, single Vs dual exhaust, altitude and any other changes from stock including oil-burning or a motor rebuilt to non-stock specifications (lowered compression, different camshaft and pistons). Also note that Chrysler specified NON-resistor sparkplugs but with resistor wires. Most counter guys will give you resistor plugs (and non Champion cross-ref'd plugs the same). While I've always run resistor plugs (it seems to make little difference), those of you all still getting by with points-style ignition might notice a slight difference, as resistor wires with resistor plugs have more, (you guessed it), resistance. My preference in sparkplugs has been Bosch for over fifteen years, especially their extended-tip Platinum plugs which are of a superior design to the competition. The primary electrode is but a single slim silvery dot at the ceramic end, causing the plug to operate over a wider heat range and reach self-cleaning temperature more quickly. I've found that a normal Champ, AC or even an Autolite Platinum (not the Double Platinum) will go but 4-6000 miles in an oil-burning cylinder, whereas the Bosch will go up to 20,000 under the same condition. The design pretty well prevents gap erosion over the life of the plug, saving wear and tear on the balance of the ignition system. I've found no benefit in using Splitfire plugs, but look forward to trying the new Bosch Platinum +4 whose secondary electrodes replicate a type of sparkplug used in piston airplanes for many years. (Norm, what're you running in that Lycoming?) 


Prior to installation, I jack up the car on stands as access to at least three plugs on my car (71 Newport) is terrible from above. Let her cool down, obviously, and get out the torque wrench as installation is generally 12-20 ft/lbs. I also use a wobble or swivel adaptor, several extensions, and a deep socket made to be used with plugs. Each plug should not be assumed to be "gapped from the factory" as there is always a deviation of at least . 003 across the (8) to be installed. Use ONLY a wire type feeler gauge set (spark plug tool with accessories), and just trash the key ring disc type and put the flat strip gauges back in the toolbox. Adjust the secondary electrode from the back, gently, and be sure it is EXACTLY centered over the primary as well as being even front to rear across the primary. Use your wire gauge to run the bent portion in between the two until you can feel just the slightest "snap" to know you have the gap exactly. If I am running . 035 gap, I adjust the plugs for the cylinders with the lowest compression (you did do a compression test after removing the old plugs, right?) to the tightest gap possible, sometimes going down to .032 as the ignition will have the hardest time with this (these) cylinder(s). After gapping, I spread the smallest amount possible of Anti-Seize Compound on the threads, taking care not get any on the lower threads near the electrodes or on any part which will "see" the combustion chamber, as this can induce a local hot spot promoting pre-ignition. You may ask if this is necessary for an iron-headed engine (it is mandatory for aluminum-headed ones), and my reply is that I never have a problem in removing a plug so treated. Plus it has the added benefit of making a plug run a little hotter (the anti-seize sets up a slight barrier to dissipation), excellent for my 1500-mile per quart motor (which might be even less if I fixed a few leaks), keeping me from changing heat ranges. I now use FEL-PRO Copper-based Anti-Seize as it lessens this tendency to near nothing. (But the Bosch Platinum operates over at least 4 or 5 Champion heat indices, so it doesn't much matter.) Then, a good smearing of Dielectric Compound on the terminal where the high tension wire attaches, screw the metal gasket (washer) in place and I then replace them in their original packaging until the moment of installation. Remember, if you drop a plug, do the gap all over again. 


I consider spark plug replacement to be just one part of a tune-up, but never without a more thorough check of the secondary ignition system. It is not unusual to find a high tension wire with frayed, bloated or broken covers or boots. Heavily P-O-L soaked ones are no good either. I always replace them as a set. Another IML'er says he uses solid metal core wires, I generally use better than parts store sets as they are unnecessarily cheap, preferring 50-ohm resistance wires as available from Summit Racing (variety of manufacturers) which cause no radio noise. But as MY radio is currently on the bench, I'm thinking of using solid metal wires just to mess with the too many loud stereos their owners think I'm trying to listen to when at a stoplight . . . and I shall listen to my motor rev across their overly expensive systems this summer. Maybe I can cause a few Bimmers some computer woes; hmmm, any comments from EE's out there on RF lock? Remove the coil wire (good safety practice), and remove all the high tension wires by pulling on the boot, not the wire itself. I get out the brake parts cleaner aerosol and spray a cloth rag to wipe down the wires, reattach them to the retainer clips and lay them out in order to not get mixed up (but keep a copy of the firing order handy nonetheless). One can pull a plug/wire each at a time, I prefer to do one bank at a time. A compressed air source should be used to clean the area around the plug prior to removing it (I usually use an old toothbrush kept just for this nasty job, followed by a blast from the portable air tank). I check for corrosion at both ends of the high tension wires, clean out any in them or on the cap itself (after investigating the condition of cap and rotor), and generously apply more Dielectric Compound. (I often pull the battery cables, clean the battery terminals and them and apply yet more.) Then, the empty spark plug threads should be "chased" with a sparkplug thread chaser to remove all the crud which can accumulate, followed by yet another blast from the air tank (or a little work with the small opening attachment on the shop vac) to keep everything out of the cylinder. Some folks oil the threads in the SP hole at this point with the new plug, but I much prefer the Anti-Seize Compound as it has excellent lubricating properties which are corrosion-resisting in ways ordinary motor oil is not. Once the plug is installed until snug (not tight) I use the torque wrench to establish 15-20 lbs/tq, really only seeing to it that I have all of them tightened evenly, and that they will not back out or loosen. Any Chrysler specific tips out there? 

Tip from Steve:

Those "tough-to-change" plugs....I have changed a few plugs in large, Chrysler products over the last couple of years,15+ years actually....and I have found that to assist screwing in a plug, I will slip a straight hunk of fuel-line over the ceramic portion of the plug...then try to screw it in. This is especially helpful if the exhaust manifold is hot.

I can't say that I have ever had a real problem changing plugs with the right tools....nor have I ever had to jack-up a Chrysler or Imperial to change plugs.

These are the tools I would grab: 1) A decent ratchet or two. Preferably one with a small handle, and a longer one with a tilting head. 2) 13/16 spark-plug socket with the "hex-head" on the end so you can slip a wrench over the end of the socket. (most s-p sockets have these) 3) A wrench to slip over the end of the socket listed above. 4) 1,3 and 6 inch extensions. Preferably the "wobble-end" kind. 5) A few hunks of straight, rubber, fuel line to start the plugs in their threads.

Tip from Jay:

I realized last month, after reading an article in Cars & Parts, that my Imperial's spark plug gap was not to factory specification. It seems that the tool that I used to check and set the gap (the round, silver dollar size spark plug tool) is highly inaccurate. It seems that the tool, which has a tapered "wedge" that circles the tool along with a gauge for measurement reference, was correct BEFORE the damn tool was chrome-plated by the manufacturer. The plating, which adds about .003" per side, was subtracting a total of .006" from the spark plug gap. If you use this tool to set your gap, you will be setting the gap .006" too large! BEWARE OF THIS EVIL TOOL! Since I haven't had the time to reset the plug gaps, I am reminded of this inaccuracy whenever the engine pings.  I also think of the gas mileage and power that this is costing me. 

Tip from Lee:

Over the years in the mechanical business I have seen defective spark plugs. This is possible if you have only lost one plug, inspect the remains of the old plug and check to see if the ground electrode is in normal condition .Inspect the end that the porcelain normally protrudes from and you will probably find that the rolled edge that holds the porcelain in is not torn away ,but just was never rolled properly. Over the years I have seen two Champions do this... I use AC now.

Tip from Todd (1981-1983):

The plate on the inside of the front end (under the hood) stated that the gap for the 5.2L 318 EFI should be .035. So I did as the plate said. This was prior to receiving my service manual. The book said to gap the plugs at .048. The .035 was for carbureted engines. When I regapped the plugs the car ran beautiful and smooth. The smaller gap made the car stalled after start-up.

Tip from Dick (1981-1983):

The only safe way to check for spark is to take a spark plug, connect it to the coil secondary wire, just as if it were going to the distributor cap, then lay the spark plug on the engine in such a way that the outer metal part of the spark plug is for sure grounded, then crank the engine and watch for the spark at the center electrode. This will limit the high voltage to 10,000 Volts or so, which will not cause any catastrophic failures in your electronics. You got away with it this time, but don't do it again, or I will rap your knuckles! The FSM tells you not to do this, but they don't explain why. This is similar to the reason they made me turn off my cell phone the last time I flew on a plane!

Tip from John:

I'd be REAL careful about pulling plug wires at the cap with engine running. If you accidentally dislodge the coil wire or the plug wires are really bad, you could get the shock of you're life. Been there done that.

AND Steve:

To substantially lower the risk involved in pulling off spark-plug wires one-at-a-time to check for a dead cylinder and getting SHOCKED, lean over the cars' fender w/o touching the car. Using 45' spark-plug boot removal pliers helps too. If the car runs the same when you unplug one of have a problem.

Follow-up from Norm:

Let's not get carried away, here. If you are working on an old car without "High Energy Ignition" and you are careless, you can get a jolt but it will not knock you in to another time zone. Start (with the engine and ignition off) by making sure all the plug wires are securely inserted in to their respective nipples in the distributor cap. Then, start the car and carefully remove one at a time. It is FAR easier to do it this way than to go to each plug with a plug wire pliers and pull them off, especially if your car has ac and auto pilot. Be advised that a poorly functioning CARBURETOR may give a regular miss in one or more cylinders because the mixture is different as it goes to each intake valve and may be incombustible in one or more( as I have just observed) and you will see no RPM drop in the cylinder(s) so affected.

Tip from Roger:

Old mechanics trick for hard to reach plugs. Get a section of vacum or fuel line that is long enough to reach the desired area. Place the hose over the wire end of the spark plug and you now have a flexible spark plug starter. Works great! I use this process on the old 460 furd pu. All of the back plugs on the drivers side are the pits. Remember don't force it!! Oh, yeah a magnet tip in the end works for those hard to reach bolts. The best magnets are the small round flat ones that look like a pen sold by the car quest. They have enough pull to start and thread a bolt most the way in.

Question from John:

Does anyone know where I can get those small slotted nylon wrap-around clips that hold the plug wires away from the engine?


From Elijah:

Year One has these -- You may need to get a catalog from them to find the part number.

From Joe:


Year One will charge more in shipping/handling than the cost of the parts.

Question from Kenyon:

When I turn off the lights and run the engine, spark leaks out and jumps to the block on 2 wires that are properly suspended and cleanly installed. The wires are only 2 years old and not cheapies.

Is there anything that I can do to the new ones to prevent recurrence, or was I just unlucky?

Reply from Jay:

I am having similar problems with the passenger side wires on our '62. The #8 plug wire is getting cooked by the heat coming off the manifold (passenger side, nearest the firewall) The stock "stand-off" wire holder for the #6 & #8 wires doesn't allow for enough air-space between the wires and the exhaust manifold. The #8 wire cooks to a point where the wire arcs to the manifold. I'm running the Mopar Performance electronic ignition, and the spark was jumping nearly 3/4 of an inch!

When I installed a new #8 wire, I made a heat shield/insulator for the it using a 6" piece of rubber fuel line. Slit lengthwise, you can slip the wire into the fuel line and slide the fuel line down to where it will offer the most protection.

This appeared to work for a while, but the new wire started to leak as well. This time I was desperate to find a way to route the wire farther away from the manifold and the heat. The trouble is there isn't anything nearby to attach the wire to to get it away from the manifold...

..except for the A/T dipstick tube!

This would work, but I was concerned that strapping the wire to the dipstick tube would eventually cause the wire to arc to the tube. My final mounting configuration is this:

1) #8 plug wire encased in 6" length of fuel-line 2) The "casing" is mounted to the tranny dipstick using a piece of insulated solid-core wire. (imagine an industrial-strength twist-tie) 3) Wedged between the fuel line "casing" and the dipstick tube is a 2" length of popsicle stick (this to give an extra measure of insulation/distance to prevent future arching to the dipstick tube)

Maybe I went a little overboard on this solution, but it's worked great so far.

Question from Steve:

Can someone describe to me how, when an engine jumps time, that a piston can travel farther up it's bore....enough to hit the spark plug?  I have heard of an engines timing chain or belt going bad...then the piston traveling up it's bore and contacting a valve which is open due to improper valve timing. Such a case would be in an "interference engine". Example: F*rd Escort. I believe a '59 Imp engine would be a  non-interference engine, whereas...there is enough clearance between the piston and the valves so that they can never make contact. Unless, of course, a high-lift camshaft is used and/or high topped-domed pistons are used. And even in that case, how would the piston hit the spark plug?

Reply from Dick:

The only way a piston could hit a spark plug that I can think of would be the use of incorrect spark plugs (wrong reach or wrong electrode design. Is the plug the correct one for the engine? Beside the point here, I know, but mid year 1955 Packard changed the spark plug call out from a 3/8 reach plug to a 3/4 inch reach, and some catalogs show the wrong info. The consequences of putting a late 55 plug into an early 55 engine are not pretty! If the plug is correct, then I think you got a bad batch of plugs, or else pre-ignition is causing excessive combustion pressures, which can damage many things more expensive than the sparkplugs - be happy that they acted as "fuses" to let the pressure escape before something else let go!


Does anyone have any ideas what would make my spark plugs foul too quickly?



I had a problem with fouling plugs also, turns out the valve stem umbrellas (seals) were gone from years of heat they turn hard and crumble off the valves. The new seals cost about $25 for the good ones with wire reinforcing. A good Mopar mechanic can replace the seals by charging each cylinder with compressed air and releasing the valve spring keepers to expose the seals and replace them without removing the heads. Worked wonders on my car.

From Frank:

When an engine sits idle for a while (not used at all) the valve seals almost always dry out and crack up. Engine oil then can run down the valve stems and burn in the combustion chamber. The piston rings can also seize in place, either: by rusting to the cylinder wall so that their sealing edges, when broken free by starting, don't seal anymore; or by the rings seizing in place in their piston grooves so that they don't expand outward to seal. When this happens to the lowest ring, the oil control ring, the engine will burn oil. Ring problems require a bottom end job. Assuming that the compression is good you can replace the valve seals yourself. You don't have to take the car to a mechanic to do this job. I've done it, most recently on a '76 New Yorker. Get the best quality seals that you're auto parts guy has. (Shop around to get a quality name brand.) Tools required: Compression tester, cylinder leakage tester or spark plug adapter fitting (something that you can use to put compressed air into the cylinder); air compressor; torque wrench; valve spring compressor; common 3/8 ratchet set. You don't need a monster air compressor, the volume of air flow is quite low, but the pressure is pretty high. I used my own valve spring compressor which was nothing more than a U shaped rod, bent to fit under a dowel bolted in place of the rocker arm. The U-rod hooked under the dowel and I could press down on the closed part of the U while removing the spring keepers. Worked better than the commercial tool, which I thought was a pain in the butt to use. (For a small guy, I have large fingers and this tool gave more room to work than the tool I bought. 

1) Pull rocker arm covers. Remove old gasket material. 

2) Remove rocker arm. Mark the front/back end of the arm and the locations of each bolt. 

3) Remove and mark each push rod. They must go back into their original positions. Mark also Top & Bottom 

4) Remove spark plugs 

5) Thread the fitting into a plug hole, connect the air line and pressurize to about 100 PSI 

6) Using the spring compressor press down on the washer above the spring. You may need to use a small screw driver to remove the keeper from the top of the valve stem. (The keeper looks like a cone cut in half along its longitudinal axis.) 

7) Remove the spring assembly. 

8) Remove the old seal. It may be broken, remove all the pieces you can. 

9) Install the new seal. The intake and exhaust valve seals are different! 

10) Replace spring assembly 

11) Compress spring with tool and re-install keeper. 

12) Repeat 6-11 for the other valve on the cylinder 

13) Release air pressure from the cylinder and remove air fitting 

14) Repeat 5-13 for each of the other 7 cylinders 

15) Reinstall push rods - observe original positions 

16) Reinstall rocker arm - observe original positions 

17) Reinstall valve covers with new gaskets. Don't use sealer since it can break off and migrate through the engine. Tighten carefully to just snug down the cover against the gasket. Over-tightening ensures leaks! 

18) Reinstall plugs. (Since they're out and cheap, might as well put in new ones.) If you are a belt-and-suspenders kind of guy, you can turn the engine so that the piston of the cylinder you are working on is at TDC, preventing the valve from falling into the engine. I don't think that this is necessary since these engines have BIG valves, about 2" in diameter, which at 100 PSI of pressure means that there is about 300 pounds of force holding the valve closed. If you need to put anywhere near that much force into doing this, you're doing something wrong. [ Closing force (pounds) = Pi * r ^ 2 * PSI ] First time I did this it took probably about 3-4 hours. Now about half of that.

Question from Bob:

I wanted to replace my mixed bag of ignition wires (also distributor cap, plugs, etc.). I thought it would be nice to get some modern high performance wires and bought Mag-XTS - nice heavy silicone wires, boots, etc. Except when I started to replace the old stuff, I found that these have right angle spark plug boots (rather than straight) which seem to place the wires too close to the exhaust manifolds (440). I went back to my good local parts store and the head guy agrees, but can't find anything yet with straight boots. Am I wearing this poor guy out for nothing and is my concern valid? These wires are made by Federal. Any other recommendations? Brands, sources? Or should I stick with stock wires? By the way, these wires are red & my new cap & rotor are blue! I'll be no threat in a concours.


From Dick:

As long as the wires do not come within 1/2 inch or so of any exhaust system parts, they should live happily. There are special High temp wires, which I have had to use on my 454 engine in my Pickup, but even they cannot stand contact with the exhaust header. My personal opinion: the stock wires look nicer, and work just as well. That goes for the cap etc. too.

From Frank:

If I remember correctly, the 440 exhaust manifolds are above the spark plugs. You should be able to route the boots of your wires to point *down* and away from the manifolds. The real answer, of course, is that the old ignition system on these cars (pre-80s) only needs 7mm wires. You don't gain anything by using 8mm wires. Well, anything except a headache :) Your Imperial's ignition system's secondary voltage peaks at about 35Kv. Well inside of the capabilities of 7mm wire. Newer high energy system peak in excess of 45Kv. Some system voltages exceed 55Kv! These dielectric requirements are beyond the ability of 7mm wires, and better quality materials don't do well in high heat, vibration, chemical, etc. of the under-hood environment, thus 8mm wires. Just get a good quality silicone wire set, in 7mm size and your car will be fine.

Question from Roger (1955):

My '55 Imperial has lost its "spark". The car has run from November 2003 when I got to about a month ago. I checked the spark by removing the #1 plug and with the wire attached put the plug base to the intake manifold and had someone turn over the engine. No spark was seen at the plug. I checked the coil by putting a plug with a 0.175" gap between the coil output and the manifold and got a solid blue spark. I changed the points and condenser and checked that the primary wire was not grounded when both points were open.

Another note is that I have the center portion of the dash off to repair the radio and polish the knobs of the controls. I don't know if something in the ignition requires all of the dash controls and radio to be connected.


From Tim:

If everything was working before you did the work in the Distributor and now nothing your problem must be in the distributor area. Do you have spark at any of the other plugs? Did you maybe mess up the number 1 spark plug wire? I wouldnt panic until you double check all of those. I put new wires on my '56 once and I was off 1-spot on the cap. I spent days trying to figure it out. Then one day I noticed by looking at a picture I was off on the wires.

From Paul:

If you are really careful, you can bypass the dash and hot wire the car. If it runs that way, then you know that there is something wrong in the ignition switch or in the wiring under the dash.

I had two '55 Imperials for a while. They both came from the same place. The one I kept has always been dependable since I was able to get it running. The other one had something wrong in the ignition switch. It would only start if it was hot wired, but would stay running without the hot wire after it started. I was pretty sure that the ignition switch was at fault, but gave the car away before I got around to fixing it. The guy that I gave it to tracked down the problem and it was the ignition switch, so they can, and do give trouble.

From Roger:

The checking of the switch is easy. It has four poles on it. Starting from left to right as looking at it from under the dash, check for voltage with test light. Far left (if I remember right) is the ACC. Center should always have power to it. Middle right should be the ignition or "on side". Next pole should be start position. when under the dash check each pole to the postion of the key. I will bet that when you took apart the center you had to disconnect some wires to the switch. If there is power to the on side then a wire is broken or disconnected under the dash. that power wire will go to the firewall and to the components that shut off in the car with he key. The test light will tell the story. ***Before you go there check the wire to the coil. When the switch is on it should light the tester. If it does try a coil.***

From George:

My guess is that you have the spark plug wires connected improperly.

From Ernie:

The situation is as I understand it spark at the coil wire and no spark at the plug. That leaves the rotor and the coil as the two only suspects.

I have seen rotors with carbon tracks to ground and caps the same way. Try a rotor first as your most likely suspect.

Question from Tim (1956):

Where can I get a set of plug wires for 354 Hemi other than Summit? Anybody at local parts stores have wires with the long boot for the plug?


From Paul:

I've been making my own for my '56 ever since I bought it in 1971. Pre-fab wire sets were not available for it even back then. I have always thought that this was because the bakalite towers have to be reused. The wire ends have to be free to allow the towers to be put into place.

From Don:

If I'm not mistaken, you can get them from Hotheads. I got a set from him at the Nationals a couple of years ago.

Question from Lars (1956):

Which spark plugs do I need for my 2 '56 Imperials (C73)?


From Dick:

The original number was XN-12Y. That is a Champion number. This is no longer a current number, although they do show up on eBay once in a while. There are folks who specialize in NOS old spark plugs, so if you want the exactly right plug, you'll need to deal with them.

Otherwise, just use the Autolite 65, it is the recommended modern equivalent.

From Gary:

I just bought a set of Champion RN12YC plugs for my '56. O'Reilly Auto Parts assured me that this number crossed over with XN12Y in their system. I also asked to look at an Autolite 65 to compare them. They looked the same. We shall see!

Question from Dave (1956):

I need information about plug wires and plugs for my ' 56 sedan with 354 Hemi.  Napa couldn't find anything for me and neither could the local cheap-chain. (I didn't ask about plugs. I'm sure they have those)  Right now, my car has Autolite plugs now. Are they ok? I know some like Champion, some Bosch, some whatever.  What about platinums, split fires and all that?  


From Mark:

My personal opinion on spark plugs is that if you've spent more than a dollar for one, you've spent too much. Still, I'm willing to listen to other's experiences. (The Split-Fires seem to be a lot of hooey, though. The design may have merit, but I've found the build quality to be sorely lacking....) I think the Autolites quite acceptable, and prefer them on the old MoPars for a couple of reasons. The first is because Autolites were original factory equipment. In fact, you've probably noticed the Auto-Lite label on many parts of your car. That's  because back when Auto-Lite was a separate, independent company, they supplied all the electrical systems to Chrysler Corporation. And then F*rd bought the Auto-Lite company, changed it to Autolite, and Chrysler was sent scrambling to build their own starters, distributors and such.... The second reason is a rather silly reason: The metal parts on Autolite plugs are black, like they were back in the olden days. Not that anyone's going to see those plugs in your hemi, buried as they are deep in the valve cover, under the spark plug covers, but at least on a flathead, they just lend the proper, period look. If you're especially AR, and you don't like Autolites, you can always paint your plug of choice flat black. (I've done this, too.)

From Ken:

I also prefer autolite. The platinum plugs DO take less voltage to jump the gap, so I sometimes put them in some of my vehicles as a "treat". They are probably worth while in a 6-V system possibly, although I have not tried them in any of mine. Maybe good to have if the battery is low. Possibly faster/better starting. Just paid 1.89 for a set for the 360 in my truck the other day. Won't buy split fires, etc., because of the price. I believe the price will drop when the patent runs out, but I think that plat-plugs and split-fires do about the same thing from a tech standpoint. (less voltage to jump the gap) Anyhow from a tech-standpoint the lower voltage requirement means more spark from a weak battery or ignition system, or a wider gap and bigger spark.

From Norman:

I have found that Split-Fires work great in my motorcycles. The first time I used them I was astounded at the performance increase. I put them in every bike I bought. Then I bought my Jeep w/v8. I put in Split-Fires and found 0 performance increase. I called around to some of the MC mechanics I know and found that they have had similar experiences with Split-Fire. They love them in there bikes but not in V8s or 6s. 

From My413:

I put splits in my 413 and roasted it not a week later.   Actually I had the timing too advanced but still I put the split fires in a week before it died. Coincidence...???

Question from Barry (1956):

My '56 Black Imperial has been at the motor rebuilder for the last 4 months. The shop guy tells me he can't finish the thing because he cannot find the correct "o rings" necessary to close up the valve cover. While I may a bit inarticulate about this, what he says he cannot find is some kind of O ring for the spark plug wells, something that is apparently exclusive to the hemi. I looked in my service manual, and there is no exploded view of the engine, so I can't even really describe it or come up with a part number. He wants me to find/supply this part before he can finish. Do any of you Imperial folks know what this part is, where I could find it, or even what it is called, so I can go looking?


From Mike:

Andy Bernbaum carries the hemi spark plug insulator tube seals for $1.50 each. 315 Franklin Street Newton, Massachusetts 02458 (617)244-1118 You can see his catalog on the Internet--the seals are listed along with spark plugs, etc. under the "Electrical" section of his "index".

From Steve:

You can also purchase them from Kanter.

Question from Keith (1958):

Has any one got a pair of spark plug covers spare, and correct lead ends for a '58. I have discovered that my old '58 is set up wrong.


From Hugh:

Since it is going to be a long term project to find the covers, I suggest you consider leaving what you have alone. If I recall, you have some kind of rubber grommet on your car that the wires go through. I think you may find, from a technical point of view, that what you have is superior to the covers. I have seen pictures of the grommet arrangement in various places and they are quite acceptable to even the purest of the pure.

Keep scoping e-bay for the covers. Also try some Hemi specialists, like Hot Heads Hemi, at

They have a message board area, so you can post your new found need there. Do your valve covers still have the cylindrical protrusions welded on? It's into these that the screws holding the wire covers go. If you no longer have them, attaching anything will prove nettlesome at the very least.

From Doug:

I see spark plug wire covers quite often on e-bay. When you do the search don't search for "195? Imperial" instead do a search for "392 Hemi". These are parts normally sold by hot-rodders who are modifying their Hemis and want to sell all the stock stuff to make some money. In the last week I've seen original intakes, timing covers, rocker assemblies, crossovers, water pumps, pulleys, fuel pumps, valve covers, and even an entire 392 block. This might be the best way to find a set of spark plug wire covers.

Question from Rex (1959):

I would like some feedback on spark knocking or pinging on my '59. I have changed the points, checked, set and re-set the timing, and bought different gasolines. Still, I have a weird problem with spark knock on acceleration and can even hear it at high speeds. The odd symptom is, though, that the problem is not consistent. One day it doesn't ping at all, and the next day it is terrible. My mechanic thinks the distributor shaft is worn and is shifting the timing, but the car has only 75,000 original miles. Any suggestions about the cause?


From Remco:

Is the carb clean and is the accelerator pump working. If the carb is not a clean mixture, it can get too lean and get engine knock. 75,000 miles can be enough to have a lot of carbon build up in the cylinder heads because this knock can happen.

From Bob:

Have you checked your vacuum advance for proper operation?

From Bill:

Remco is right, if you have a lean-out situation due to a dirty carb, bad accelerator pump, floats set too low etc, you can get engine knock, and carbon buildup can also be a culprit. You can make a quick check of your distributor with a timing light. If you get erratic movements of the harmonic balancer's timing mark, you could have a bad distributor. If the mark moves smoothly between idle, higher RPMs, and back again, your distributor is probably alright. Watch your dwell angle too, it should remain pretty constant throughout RPM changes. Remember, dwell affects timing, but timing does not affect dwell.

And... a badly worn or stretched timing chain can also cause erratic timing.

From George:

The main cause will no dought be the poor quality of fuel available now days, and this can change between every Gas Station or between each delivery to you local Gas Station. Here in Australia they drop any old junk they have left over into the fuel, high amounts of Ethanol, old stale jet fuel, just about anything really, so I bet they do the same in the US. To adjust your motor to suit the poor fuel you may need to run a lower advance, droping it back to say 5 degrees and if you have the spring loaded Vacuum Advance you need to add some washers to keep that advance back a bit. The very simple equation is the worse the fuel, the less advance your motor can handle. I run my old Valiant ( 318 V8 ) on Propane, and because it has a higher octane than Petrol it never knocks, but if I change it over to Gas (Petrol) she will rattle it's head off when I try to work her hard.

From Paul:

I am also inclined to think that this spark knocking is fuel related. Of course not being there, I can't say for sure. In addition to everything else that others have written, I didn't see anything about the possibility of a weak fuel pump. This is another thing that could cause the car to run lean. I have discovered that the new gasolines that we have today are VERY hard on fuel pumps. If there is a tear in the diaphragm it won't last long anyway so you will know pretty soon if the fuel pump is bad.

If you are having ignition trouble, it could be as simple as replacing the points. The points are suppose to be checked/changed every 10,000 miles. This is something that we tend to forget today in this age of "no maintenance" ignition systems.

From Steve:

My first suggestion would be distributor. It is possible that the mechanical or vacuum advance are not working properly. Secondly check your timing chain for wear.

From Chris:

I had terrible spark knock on my '66 (which has very similar timing specs as '59), and after much trial and
error and endless adjustments, the problem was fixed by installing a correct, new vacuum advance. Hasn't pinged since.

I suspect the problem is that the initial timing is already pretty far advanced in early big blocks - 10 BTDC, as I recall for '59. Relatively little vacuum advance is used compared to '67 and later. Therefore, if the springs in the vacuum advance get weak, you get too much vacuum advance too soon. The result is pinging, especially on light acceleration when vacuum is highest.

Of course, you need the highest octane gas you can find, as well as proper fuel delivery in the right mixture, and the engine running at the correct temperature. Even proper timing cannot overcome lapses in these areas.

Correct vacuum advances appear on E-bay periodically. Don't buy a generic from NAPA - I can guarantee you it is set for 1967-and-later specs.

And speaking of vacuum, a vacuum leak can lean out the fuel mixture, too, contributing to pinging. I assume it idles smoothly? If so, chances are there are no leaks. If it has a lumpy idle, look for a leak.

From Chris:

What kind of spark plugs are you using? If they're Champions, try a set of Autolites. They cured my problems with pinging and fouling as simple as that, and I've never bought a Champion plug again. I use Autolites in all my older Mopars and am 100% satisfied.

From William:

If what you're hearing is "trace rattle" as opposed to heavy detonation, the trace rattle can be a timing/fuel/carbon buildup/operating temperature issue. With trace rattle, if you back off the base timing about 2 degrees, it might go totally away, for example. Heavy detonation would take much more timing retard.

I would think that at just 75K miles, there should not be enough wear in the distributor shaft/bushing interface to significantly affect timing. What might be more important is the wear on the breaker cam in the distributor and related lobe-to-lobe differences, which can cause the timing to not be consistent from cylinder to cylinder, but still not enough to cause even trace rattle unless things were at the "build tolerance stack" situation for compression ratio vs. fuel situations.

Remember that all breaker points NEED to be lubricated when they are installed. I've run across modern point sets that seemed to delete the little vial of lube and without the necessary lube for the rubbing block of the points, the rubbing block will wear prematurely and cause the dwell reading to change and with it, the base timing setting. Point lube is still around, though, even if it's in the General Motors Standard Parts Catalog.

The item regarding the vacuum advance unit might be worth checking out too. Usually, though, if they fail, the rubber diaphram will rupture and cause a vacuum leak. If the timing does not advance sufficiently under cruise conditions, fuel economy will be in the dumper pretty quick and throttle response will similarly suffer. Not to mention the vacuum leak upsetting the mixture. A retarded spark can lead to higher operating temperatures too. It's pretty easy to stick a plug in the vacuum line at the vacuum advance unit to see if that makes any difference, just don't forget to pull it out when you determine that's not the problem. Of course, they're pretty simple to replace so if it hasn't been preplaced, go ahead and get that done.

Now, once you get to that point, be sure to check the advance weight springs inside the distributor. Might be that one of the springs has broken and that particular advance weight is slinging out to the full advance position at any speed. That would lead to over-advanced timing for the rpm being run and could well cause the detonation problem.

A dirty carb will usually run rich rather than lean. When the air bleeds get gunked up and partially closed up with deposits, that send that circuit to the rich side of things. Where the lean situation can come in is when hard crystalline deposits might build up in the fuel feel tubes in the venturi cluster. Those can be pretty easily removed with a small twist drill, going just until you "hit brass", but you have to know where to look.

One other thing that might be more difficult to track would be if the harmonic balancer, with the timing mark on its outer band, might have slipped, thereby rendering the timing mark useless.

If you've run some decarboning/fuel system cleaner through the car and run it on the freeway for a couple of hours in cruise mode, done all of the other tune-up checks, checked the thermostat for correct temp operation (using an infrared heat "gun" to check the temp at the thermostat housing), and still have the spark knock, then it might be best to retard the timing just enough to get rid of it and see how much retard it takes to accomplish this goal.

The other thing would be to use some quality premium fuel (92+ pump octane) to baseline your tests. Then add some quality octane booster to the mix and see what happens. Another alternative would be to get 5 gallons of genuine racing fuel to add to one tank of your super unleaded fuel.

Back when the fuel ratings and unleaded fuel came into the mix, I determined that 95 posted pump octane equated to 100 Research Octane rating, which most of the premium fuels (i.e., "Ethyl") used to be at their peak in the middle 1960s. Similarly, the current posted octane rating of 93 should be pretty close to the 97 Research Octane Rating that the original B/RB motors were specified with in 1957. Using a quality brand in current times is more important that in prior decades, I suspect. You can still find 100 Research Octane rating unleaded fuel through Union 76, Sun Oil, Phillips 66, and similar racing fuel vendors.

If your rattle is determined to not be from fuel issues, it could be due to heat situations inside the engine. For example, if the rear core plugs haven't been knocked out and the system given a good cleaning/flushing, localized heating (in spite of a normal temp gauge reading) due to poor coolant circulation could be an issue.

I suspect that only a systematic diagnostic strategy can really find out what the cause is. In the mean time, getting quality fuel into the system and backing off the timing a little might be the best things to do.

Question from Jeff (1959):

I am in the process of repairing the problems with my 392 Hemi.  I have found one broken wire inside the distributor, and there were broken pieces of black plastic inside the distributor which we took out. Overall, the inside of the distributor looks kind of sick.  I have heard from some that I should get an electronic ignition conversion for it and dump the old distributor innards. I have also heard that the 392 hemi-dual point distributor is a wonderful unit and should be fine. We have also heard that there is currently no electronic conversion for the dual point distributor. What should we do???? Get this one repaired or replaced or is there an electronic one available for less then an arm and a leg. 

Reply from Bill:

 In my opinion, I would go to the electronic ignition. Call Year One (800-YEAR-ONE) and ask for one of there tech advisors. I'm sure they can set you up for around $150.00. If you are looking for a Concours restoration, you may want to have yours rebuilt/replaced. A used replacement will most likely have to be refurbished also, however. I may have some names of distributor rebuilders at home, if you need them. Once you have tried the electronic ignition I'm sure you will very happy. The one you should get is the authentic MOPAR orange box!

Question from Clay (1960):

Would anyone know the correct Autolite plug for my 60 Custom?

Reply from John:

The correct Autolite plug is #85.

Question from John (1961):

I tuned up our '61 Imperial today, but ran into a dilemma when I finished. The car now won't start. I'm not sure if I got a spark plug wire in the wrong place or what, but really need some quick help with this problem. I have to park the car in front of our house on the street, but this Thursday the car has to be moved for street sweeping. If not, I'll get a ticket..
I know the spark plug set up on the 413 is (left) 1,3,5,7 and the (right) is 2,4,6,8. My question is the left the driver's side?? Also does anybody have the wire placement on the distributor cap itself starting the 12:00 position and going clockwise with the wires?? The car cranks, but now it doesn't start.  I put a set of Champion RJ12YC plugs in the car. The originals were RJ10YC plugs..


From Dick:

First we need to determine if the distributor is clocked right to the camshaft.  As you are probably aware, the engine turns two revolutions for each revolution of the distributor. Thus putting the distributor back by simply lining up the timing mark with the pointer and dropping it in so the rotor points at #1 plug wire gives you a 50-50 chance of getting it exactly backwards! Spitting back through the carburetor when you prime it means that a spark plug is being fired when an intake valve is open, so I'm betting you are 180 degrees off with the distributor. Don't get mad now, this happens to all of us! 

Forget all about trying to start the engine for now, in fact, pull the ignition wire to the + terminal of the coil loose, so you won't get your eyebrows singed!  

Then, take #1 spark plug out (on a 352, this is the front plug on the PASSENGER'S side). Put your compression gauge in the plug hole, or if you don't have one, get someone to put his or her finger over the plug hole, while you manually turn the crankshaft in a clockwise direction until pressure starts to build up in the #1 cylinder. The crank will be hard to turn, but do it by hand (put a long wrench on the crank pulley bolt) or you will miss the pressure pulse for sure.  

When the helper or the gauge starts to detect pressure building up, stop right there and look at the timing pointer. Now, slowly move the crank in a clockwise direction (from the front of the engine) until the pointer is exactly on the top dead center mark on the pulley. Now, without moving anything, look at the rotor in the distributor, and determine which plug wire hole it is pointing at. If it is pointing at #6 (the 3rd cylinder back on the DRIVER'S side), you have the distributor in backwards. If it is pointing at the #1 plug, you have it in correctly.  

If it is close but not exactly on the #1 plug wire hole, you may be able to adjust the distributor to make it run OK by rotating the distributor while you watch the points open. The right setting (or close enough to run the engine until you can get a timing light on it) is when the points just barely start to open when the crank is where we just left it.  

Once you have determined that all is shipshape there, probably the engine will start up and run for a few seconds each time you put a few squirts of gas down it's maw. Don't over do this, we don't want to wash all that oil off the cylinder walls. The safe way to do this is to put the air cleaner back on loose; leave the wing nut loose a few turns and prime the engine by putting small amounts of gas in the depression in the center of the air cleaner lid (if it has one). The gas will run down the center screw and get to where you want it to go, and you won't have to worry about any flash back from the carburetor.  

Don't forget to hook up the ignition wire! 

If after running the engine for a minute or so total this way, the fuel pump still won't pick up and start pumping the fuel from the tank, you may have to take the fuel line loose from the carburetor, and using a small squirt bottle or oil can, pump the carburetor float chamber full of gas, then reconnect the line and let the engine run until the pump finally catches its prime and starts pumping on it's own. If it absolutely won't run on it's own, you must have a pinhole leak in the line from the tank, or a weak fuel pump. Get a pressure gauge on it, and see if you are getting 3 to 5 PSI out of it. If so, let it pump gas into a coffee can while the engine is running (fill the carb with your squirt bottle again and start the engine), to see how much gas it will pump in 15 seconds. It should about fill the coffee can in 15 seconds. If it doesn't, it's fuel pump time, sorry.  

From Mike:

The firing order for your 413 is 1-8-4-3-6-5-7-2. This should be the order of the spark plug wires on the cap going COUNTER-clockwise. The cylinders are numbered: 1-3-5-7, from front to back on the DRIVER's side and 2-4-6-8, from front to back on the PASSENGER's side. What all did you do on your tune-up besides change the plugs? Did you change all the plug wires (and, if so, all at the same time)? How about points, rotor, cap, condenser? Did you set the timing at all (i.e., rotate the distributor)? I guess I would suggest first locating the #1 plug wire on the distributor cap, and trace the rest from there going counter-clockwise to make sure the relative order is correct. If it is, and you changed all the wires at the same time, then it's possible that they're all off by one position, in which case you need to rotate the engine until #1 cylinder is at top dead center (TDC) on the firing stroke, remove the distributor cap, and make sure that the rotor is pointing close to the terminal where the #1 plug wire is attached. Write back if you think this might be your problem and you need clarification, such as how to find top dead center, or if you have any other questions about other possible causes. 

Follow-up question from John:

Yesterday I ended up changing the plugs and all of the wires. I didn't due to the points. I bought the wires at Napa, but when I got home I didn't realize they were the kind you have to make..I had never made wires before, so I took an old wire off of the car and took it apart to figure out how to make the plug wires properly.
I did each wire, one at a time and checked them 3 times when I finished.
My question is, when you are on the passenger side of the car looking at the distributor cap, and starting at the 12:00 position and going clockwise from twelve, what is the order of the plug wires on the distributor cap itself?? What position is number one at on this cap?? I didn't see any number 1 marked on the cap.. I think if I have any wires off at all, it may be two..I also need to know is the number 1 plug at the very front of the driver's side of the motor...When you turn the car over, it cranks and kind of has a puffing sound coming out of the carb..I never set any timing on the car or did anything other than changing the distributor cap, rotor, plugs, and wires...My other problem is I don't have any gauge to tell me when the number 1 plug is where it should be..

Reply from Roger:

THERE IS NO 12:00 POSITION.  If you line up the word "front" in the diagram below you will see the relative positions.  Between #8 and #4 and between #7 and #5 are the clips.
F         1 2
R    8          7
0    4          5
N         3 6

Reply from Mike:

There are numerous ways to go about finding out where your plug wires need to go, it's probably simpler to give you an illustration--go here for an illustration showing the orientation of plug wires into the distributor cap. 

Question from Dennis (1962):

My '62 had bosh plugs in it & they are terrible. Can someone tell me what the original plugs or a better one to use?


From Paul:

Spark plugs usually don't fail unless they are too old, or there is something else wrong with the engine. What did they do that leads you to say that they are terrible?

In my Imperials I use Autolites. They aren't the best quality out there, but in those cars they are suppose to be changed every 12,000 miles anyway. They have worked fine. I have learned not to start my cars unless I plan to drive them someplace. Starting the car and letting it idle will fowl the spark plugs in a hurry.

Spark plug replacement is interesting to me particularly on cars that I drive a lot. That is because as you say, the condition of the plugs when you take them out is VERY revealing. If the cars just sit around a lot and only get started occasionally without being driven this will tell you next to nothing.

Most generic shop manuals give a page or two of color pictures that show what various plug conditions indicate.

From Keith:

I have been "listening" to all the discussions and comments on spark plugs and thought I should throw in a couple of my pennies. Recently, I have been fooling around with my timing trying to get rid of some pinging. The only way I could get rid of it was by retarding the timing :( Then, I came across one of my Grandfather's old Petersen shop manuals (1975) and it says, "Plugs with PLATINUM or other fine wire electrodes and surface gap plugs having no side electrode should not be used unless specified by the manufacturer." Guess what kind of plugs I took out of my car? I now have the O.E. champions J-13Y and my timing is no longer retarded. The '66-71 used the same plugs (J-13Y) and '59-'65 used J-14Y; '72 used J-11Y all of 'em are gapped .035". So I have to agree with Paul, unless the plugs are old or something is wrong with the engine, plugs don't fail. In fact, according to the same book, plugs are an excellent indicator of what is going on inside the combustion chamber.

Anyway, whatever works for ya'-- Do it!

From Chris:

Older Mopars (in fact, well into the 1990s) don't like platinum plugs, Bosch or otherwise. Try Autolites. #85 is the Autolite spark plug model number.

From Eric:

I have had good experience w/NGK plugs. Their threads are machined so that they seat squarely into the head when installing, under and angled up behind the exhaust manifold as they are. They seem to be durable enough, though any motor with a worn timing chain / nylon cam gear will foul an otherwise good plug. The previous few thousand of miles before my nylon cam gear failure, I would have a fouled plug just days after replacing them. After the new chain / steel gearset, and a thousand miles, plugs still fire ok. Thus, your actual MPP may vary.

From William:

Chrysler's OEM plugs were either Champions or Prestolites back then. Without looking, I suspect something on the order of a J10Y or J11Y Champion gapped to .035" would be reasonably close to what the original plugs were. Some of those colder Champion plugs might have gone out of the normal sales channels, but I think Mopar Performance might have some in their catalog.

Bosch has a reasonably good reputation for quality items, but when I tried a set of Bosch plugs in my '70 Monaco 383 4bbl in the early 1970s, they did not last nearly as well as the Champions or Motorcrafts I used back then, so that experiment ended. Had a similar experience with SplitFires in my '80 Newport 360 2bbl--they ran no better than the NGK V-Power plugs (in spite of costing nearly 3 times as much!) I had been using or the Motorcrafts that I put in it when I got the car (used).. I've even waited on some customers who bought Bosch Platinums and wanted the OEM plugs to go back in their vehicle so I'd run ok again. Personally, I'm not a big fan of Bosch plugs, but have had good luck with Champions, NGK, and Motorcraft as far as lasting a long time and being trouble free. Others in here also seem to like the current Autolites, which is fine.

Question from Ken (1963):

I have been trying to replace the spark plug wires on my 1963 Crown (413 c.i.). The old ones have straight ends where they attach to the plugs, but the ones listed in the parts store for a '63 have a 90 degree bend. It seems to me that the straight ends would work better, since they keep the wires away from the exhaust manifold, so I am reluctant to buy new ones. Does anyone know which ones are "right"?

Reply from Bob:

I went through the same problem 6 months ago and wound up with some heavy duty orange wires with a Kevlar core. It's an obscure brand. Cost about $36 and work fine so far. After I bought these, I found a speed shop that was carrying Mallory wires with straight ends, about the same price. New on the market are truck/RV wires with special ceramic plug covers to protect against heat. These look interesting. I think the straight ends are a good idea.

Question (1966):

Does anybody have any suggestions on what type or spark plug to use on my 1966 Imperial with a 413?

Reply from Ross:

In re the gentlemen looking for plugs for his 66 Imperial. I forgot yesterday to state that my 1972 era CHILTON REPAIR MANUAL covering 1965-72 American automobiles, indicates that: Champion J11Y is indicated for this application. If the plug you're given by the parts man has an R designation, then this plug is a resistor model, which Chrysler did not specify as OEM. Have the correct parts ordered if authenticity is the name of the game, as resistance wires AND resistor plugs sets up too much resistance for the coil, leading to premature points wear. However, my info is old. Contact Champion for latest information about your SPECIFIC application. The plugs I pulled from my car this past week at 18,900 miles showed substantial oil/ash deposits which I need to correct by replacing the valve stem seals. Were I the type to buy from Year One the correct date coded spark plug wires (correctly, high tension wires), I'd be contacting Champion about my attempts at changes in initial and overall timing with the carburetor and exhaust system I'm now running to avoid pre-ignition on the poor quality gasoline of today. Mine's a daily driver and long distance runner, not anybody's idea of a showboat (which is why I don't worry about authenticity.) My spark plug needs are different from yours. I run the Mopar Electronic conversion package (with orange box), 50-ohm resistance after-market high tension wires, and run Exxon 93 octane exclusively with the occasional addition of 105 octane/4-grams gallon leaded racing fuel in a 10% mixture. Reading spark plugs is much more than a science as any serious racer will tell you, it is an art. Small things can add up to a big difference here, please don't be put off by all this, but consult directly with the manufacturer.  My experience is that extended tip plugs (Bosch Platinum) alleviate other conditions FOR WHICH I'M WILLING TO ADJUST OTHERWISE as they are felt by many to induce hot spots aggravating pre-ignition. I change the vacuum advance rate to compensate, as I value the self-cleaning properties more highly. Finally, nobody, but nobody has the experience or technical wherewithal to match Champion.

Question from Rob (1967):

I'm in need of a little Imperial guidance here. I've been working on my '67 Le Baron trying to get it back among the living after its 15 year coma. The Holley that was on it was pouring gas better than a full service pump. I've pulled the Holley and installed a spare Edelbrock I had here, but I need to change the plugs. Is there a trick to removing the rearmost driver's side plug? The steering column coupler is in the way. I also notice the front passenger plug caused some clearance problems with my ratchet and the upper control arm hardware.


From George:

I have found on most the mid/late 60's big blocks, getting that rear plug from underneath is usually easier.

There is no good way to get at them... its a pain.

From John:

On my '69, there are also clearance problems with some of the plugs. To service them all, I used everything from a plug socket that allows an open end wrench to be fitted to it, a ratchet with no extension, a 3 & 6 inch extension. whatever it took to get in front of or past the obstruction.

From Mikey:

This spring I had the pleasure of witnessing Leslie change the #7 plug on her '67 Imperial. I can tell you that a spark plug socket thats not excessively long and thats been broached on the end to accept an end wrench will work very nicely for this. You place the socket over the plug, use the end wrench to initially loosen the plug and once you get the plug out a few turns you can then turn it out the rest of the way by hand using the socket.

It is extremely difficult to find a combination of ratchet and extension that will clear the steering column and manifold at this particular location. I had half a dozen different extensions, sockets, ratchets, ujoints and adapters with me and the most effective tool we used was the combination wrench and plug socket.

I would doubt very much that the T handle wrench would ever clear the column of a '67, as the steering column jacket is extremely close to the manifold at this point. None the less, it CAN be done with a bit of patience.

From Eric:

I, too, was present for the #7 plug change, done by the Lovely Leslie on her Haze Green car. While everyone was gathered 'round for this surgical operation, I could be heard muttering in the background, 'just lift the motor'. Did anyone listen? Well, they were under that car for a while.

I have an Imperial-like, optional 440 in my '72 Newport. In that the dimensions for the two cars differ in exactly this location of the #7 spark plug, with its 4'' ahead of firewall extension in the Imperials, I will offer the caveat that your actual procedure may vary. With that said, the #7 plug in my otherwise very Imperial-like Newport is impossible to change either from on top or from under the car. My car has the Imperial-like, optional, tilt-telescope steering column and the heat insulator they use on those blocks the #7 plug. On my 1st attempt at changing #7, I ended up breaking the coupler by turning the steering wheel w/o the motor running and the coupler only partially attached, this after removing the heat insulator.

A FWD GM driving 'acquaintance' of mine looked at the situation and said, 'just lift the motor'. Well, being a GM-head, maybe this is common practice for them.... anyhow, one left motor mount bolt removed, a couple of heaves on the hydraulic jack under the oil sump (w/block of wood, of course) and presto, easy access to #7.

When I do plugs now, I haul out the socket that fits the motor mount bolt (this is the long, lower bolt that threads into the subframe) my jack and block of wood, and my thin walled spark plug socket. Simple procedure. End of story.

From Mike:

I once had a BMW 2002 (from 1971...go figure) that needed to have the walls of the socket ground down to give enough clearance to get around the plug. While that car has long since gone from my stable, the socket remains in my toolbox, and has proven its worth
once again with this #7 plug. Having a slightly thinner wall on the socket makes getting around the plug easier. The weakened socket isn't really an issue, since you shouldn't torque plugs too tight anyway.

From underneath is the best way, a wrench on a hex-ended socket works but my craftsman ratchet is thin enough profile so that it will work, too. You put the socket on the plug, and the ratchet on the socket, swing a couple of turns, ane take the ratchet off and spin by hand.

When my arms were thinner, I could snake then underneath the brake booster and do the operation from above. That'll teach me to work out!

From Bill:

The rear most plug on the left side of your car is best removed from below. More than likely the reason the right front plug is hard to remove is that over the years the motor mounts have compressed, which reduced the clearance.

From Mike V.:

The way I used to change the #7 plug on my 72 New Yorker was to use a 13/16 socket with a 7/8 HEX END that you could slip a box wrench over and "out comes the plug". Then of course you had to fanagle your fingers with the plug from underneath of the car to get it started, but you would tighten it up the same way. Craftsman or S-K Tools should carry a spark plug socket of this type.

Question from Demetrios (1967):

On one of my '68's, the plug wire of the rear cylinder on the driver side bank came loose while driving. I think the reason is because I did not push it in properly when I installed it. I can't access it from above to push it hard enough. The question is, is there another way that works with this plug wire? I tried to reach it from under the car after removing a sheet metal cover, no way. Is it more accessible under the fender after removing the front tire? Before I spend the time and effort and time trying, I hope I can get some suggestions from people that have faced this problem before for '67 and '68's...

Does anybody have experience with a plug wire pliers?


From Robin:

I don't know about the '68 but on the fuselage cars I put the car up on ramps so I can work on the rear plugs, especially the drivers side rear cylinder. And as the plug wires run under the exhaust manifold to get everything just right you pretty much have to work from top and bottom.

From Roy:

Replacing that plug is difficult, but attaching the wire shouldn't be too much trouble. Approach it from the front of the car, use a footstool if you have to, but lean in on top of the engine and brace yourself with your left arm while reaching down with your right.

From Joe:

I managed to squeeze my hand between the steering column and the various linkages and was able to change that plug and get the cap back on, too. I have the scars to prove it. I love getting 75% of the job done and realizing that without a divine act the last 25% won't be possible unless you have a lift.

From Chris:

My experience with Mopars of this era is to jack up the car until the wheel clears the well, and then you can reach in through the well with a long extension in your socket wrench. I never have had to remove a wheel though.

I had the same problem with my '62 Imperial and a brand new set of Federal spark plug wires. The car ran like a dream for the first few minutes, and then it felt as if it were running on some cylinders. I reached in there and noticed three plug wires had come lose (boots still around the plugs). I put a dab of conductive grease on the insides of the boots and replaced them on the plugs. This has helped my problem.

From Dick:

I have used plug wire pliers, but only to remove the boots when they are stuck on the plugs. I doubt you'll have much luck getting them on a 440's #7 plug. By the way, when you are reaching down there, be VERY careful not to put any pressure on the brake booster vacuum hose. Those plastic check valves get very brittle with old age, and you don't want to snap one off - that will ruin your whole day

Question from Ken (1968):

Where exactly are the plug wire looms attached to a '68 engine? I have been looking at photos, but none were taken close enough to show me where to bolt these parts.

Reply from Roy:

There is a 4x clip on the thermostadt housing holding the driver side wires. Three of the driver side wires go under the AC compressor and down the front of the block to a 3x clip put on with the first exhaust manifold bolt. The fourth driver side wire takes a shortcut diagonally behind the AC compressor to a 1x clip welded onto the inside rear of the driver side valve cover. The fourth driver side wire continues down and around the back of the valve cover to a 1x clip attached to the last exhaust mainfold bolt. The first two passenger side wires go down the front to a 3x (same as driver side) clip put on with the first exhaust manifold bolt. The other two wires go to a 2x clip welded to the outside of the passenger side valve cover and are held in place with two special nylon split bushings (grommets). I have a list of the actual wire lengths at home along with which one had a straight or angled boot at the distributer cap.

Question from Bob (1969):

I have one more spark plug to put in a '69 imperial 440. Can't get it in NO WAY NO HOW! I think the threads are bad. When I pulled the old plug out, it was all right but after I put some transmission oil down the plug hole, it must have gotten something in it.  I have been trying for three nights now and no luck. Is there a easy way to solve this problem?


From Bob C:

Let me guess, the number 7 plug, left rear under the exhaust manifold with the steering column in the way? If it is the trick is to come up from the under side of the car. It means jacks or a lift or ramps and then still not fun. If it is not the number 7 plug let us know and maybe someone else can come up with some other idea!

Follow-up from Michael:

If it is #7, the FSM for my '72 New Yorker (sorry, but they are close) specified how to reach each plug. #7 was from underneath, using a 13/16ths wrench. It made an otherwise impossible job almost tolerable

From Todd:

When I changed my plugs on my '68, I too had a hell of a time with the #7 plug. I didn't have a jack or stands, but fortunately my roommate had a highly extensive socket set. With the right combo of hard to reach extensions, I was able to get at it from the top. Not easily, but manageable.

Question from Terry (1971):

I am changing spark plugs in my Imperial and they are tough to get to. The three front on the driver's side I have changed, the last one is going be TOUGH, and the passenger side, GEE I don't even see them.  Any tips?!

From John:

This is probably like the '69, I have a spark plug socket that has a hex end on it so it can be turned with an open end wrench. I found this works well on the passenger side.  Also, I have removed the right front wheel to get at the passenger spark plugs and have worked from under the car.

From Brad:

On cars with air conditioning, I usually go from the front and sneak my hand under the battery tray/around the power steering pump.  Then again when I said I can get anything from the top, I never said I had my feet on the ground. Main reason I like working on this baby, I can stand between the block and radiator on one side of the fan or kneel on valve covers.  Much easier to reach certain things if you change your position.  Like being on the motor and leaning over versus next to it and leaning in.  

From My413:

I always have luck doing this job with a swivel socket.

From Stevan:

According to the FSM removal should go like this. 

plug #                       removal            socket & tool              caution 

1                                  top                      ratchet 

3                               bottom                box wrench 

5                               bottom                box wrench 

7                               bottom                box wrench            disconnect battery (live starter) 

2*                       top or bottom               ratchet 

4                         top or bottom                ratchet 

6                               bottom                     ratchet                avoid heat riser valve 

8                               bottom                     ratchet

*Imperial from under right front fender

Question from Chris (1972):

Which autolite sparkplugs are the ones I need for my '72 Lebaron? I've got both exhaust manifolds off, and I can actually see the sparkplugs for a change--thought it would be the ideal time to get rid of the champions that are in there now...

Reply from Elijah:

Autolite 85 is what you need for your '72. They sure work great in my '71!

Question (1973):

My 440 engine is misfiring.  Can anyone tell me what the  problem is?


From TJ:

Mine turned out to be the sparkplug wires. Plug 2 boot split and arced into 4 and 6. 3 and 6 plug boots were so thin as to be useless. These were lifetime wires with 12k, supposed to be good. I assumed everything else but the wires. Talk about feeling like a cherry. Question does anyone have any recommendations for spark plug wires for a '71 Imperial with the 440. Also does anyone know the path, I can't find a picture anywhere.

From Elijah:

Year One has the correct plug wires available in their catalog -- you can even go hog wild, spend some extra money, and get wires with the correct date stamped on them! Go to and ask for a catalog! Your local Napa dealer should also have a good set available, too.

From Ron:

If you do not plan to use the original type, I recommend a good set of silicon wires that will take the heat and not burn out if they touch the manifolds.

From Bob:

The wires run behind and under the exhaust manifolds. There should be wire looms/holders to direct them in the right direction....on the later cars it is more difficult to see with all the "stuff" they hung on the 440. On both sides they go down the front of the block and meet the plugs....except for the back cylinders that go on the intake manifold side of the valve covers...there should be a holder on the back of each valve cover to hold the wire in its proper place....check some of the Mopar magazines for pictures of stock earlier big blocks!!!

Question from Mark (1974):

Any suggestions on the best plug to put in my '74 440?


From Kerry:

Well, AC has been pretty religiously trashed by many folks. Champion seems to not be what they once were. I have Bosch in the '73 and it seems to do fine. I had the same symptoms as you and swore it was a carburetor problem or vacuum leak....

From Elijah:

AutoLite #85.

I'll spare you the details, but let's just say that after many years of being convinced that Champion made the best spark plugs for my Imperials, I found out that AutoLite made an even better one. :o)

From Brian:

I second the AutoLites. The only plug I will use anymore.

Question from Rolland (1981):

Most of my life (which is quite a long time) I have heard debates, participated in debates, and even defended particular brands of spark plugs. However, in all honesty I cannot say that I have ever experienced a significant difference in spark plug performance. Although I have conducted no controlled scientific tests it always seems that engine condition, driving conditions, or other environmental factors have a lot more to do with spark plug performance than the particular brand of spark plugs. Even the advertised claims of the split fire plugs would seem to have less effect than engine condition and driving factors and they are 5 times the price. 

What do you use for spark plug performance criteria? 

- Fuel economy 

- Plug life 

- Engine performance 

- Starting 

- Other? 

Spark plugs in today's engines look like they came out of the box after 40,000 miles. My 3.5L, 24 V engine in the New Yorker has plugs that look like they will run forever. However, that was not the case with the older carbureted V-8's. How do you determine that one plug is better than the other?

Reply from Bob:

I have been using Autolite Platninum for about 8 years in my '81 Imperials both EFI and carbed. They have worked much better than the Champions. Champion sure isn't what it used to be, I have had good results with the Autolites in all the cars I have worked on even for friends. I usually go a range hotter than stock since most of these cars have a fair amount of miles on them. But I have used them in new cars too.

Follow-up question from Norm:

Why hotter for a high mileage car?

Reply from Bob C:

Just to make sure that my thinking is correct about spark plug heat ranges is correct, a hotter plug means that the plug itself retains more heat from the combustion chamber, right? If the above assumption is correct, then maybe a hotter plug will run cleaner (not foul) because it will burn off the additional oil that an older engines will let pass into the chamber from worn rings, valve stems and seals. Also the cars from the '60's early '70's just seem to run richer compared to the cars of today with all the fuel injection tech. on them. Helps keep that crud off the plug too.

Reply from Rolland:

You are absolutely correct Bob. The heat range defines the operating temperature of the spark plug. Usually this is controlled by the length of the heat path from the center electrode to the cylinder head coolant. Contrary to some beliefs it has nothing to do with the temperature of the spark generated. You are also correct is assuming that a hotter plug will have less tendency to foul due to excess fuel or oil in the combustion chamber. However, consistent with the "there is no such thing as a free lunch" proverb a hotter plug will tend to destroy the electrode quicker and the probability of overheating the porcelain and cracking is also greater. It is generally best to use the recommended heat range unless oil burning and rich fuel mixtures are known to be present.

Reply from Bob:

I don't know how sensitive 4-stroke engines are to hot plugs, but it sure is very critical in a 2-stroke. A dealer installed the wrong plugs in my '63 Saab (long, long ago) and all 3 pistons got burned domes after a long run on the Ohio turnpike - one melted entirely through. Another dealer let me help him pull the engine and we replaced it all. My arrival to the east coast was delayed less than a day and the original dealer paid for most of the work.

Tips from Dick (1981 -1983):

If your car is still using the original EFI systems, there are a number of possibilities:

1. Your knock sensor might have failed, or the wire might have become disconnected. Look on the intake manifold under the passenger side, rear of the EFI system. There is a mushroom-shaped device screwed vertically into the intake manifold plenum runner headed toward #8 cylinder, which looks very much like an old-fashioned hydraulic brake light switch. This should have a wire connected to the top of it. If it doesn't, the lonesome wire won't be far away. Just reconnect it and your problems will probably go away.

The sensors themselves seldom fail. It is a simple piezoelectric crystal, and easily tested but you need an oscilloscope. Clunk it with a screwdriver, it should put out about a 300-millivolt pulse depending how hard you clunk it and how big your screwdriver is.

2. It is possible that your initial timing setup is a little too advanced. You could have someone adjust your timing to a point about 5 degrees more retarded (actually, less advanced) than it is now set at. This will positively help and probably eliminate your spark knock, but you might be putting a Band-Aid on it, rather than curing the root problem (see above and below).

3. Your car might have accumulated enough glowing hot spots in the combustion chamber from all the years and miles that you are getting pre-ignition from this cause. There is no way out of this one except pulling the heads and cleaning out the crud. One indicator to this problem is if the engine doesn't knock until it is thoroughly warmed-up.

4. Your car might be running too hot. The temperature switch is virtually useless for monitoring your engine’s operating temperature; all it does it light the idiot light about the time you smell anti-freeze. I recommend buying a glass mercury candy thermometer at your local supermarket Housewares department, removing the radiator cap (when the engine is cold!), and inserting the thermometer into the radiator fluid. Then run the car until the temp stabilizes; it should run about 200 degrees, + or - 10, if it has the right thermostat in it and everything else is right. If it runs hotter, this could be your problem. Find out why.

5. You are too cheap. Buy better gas.

If you are not still running the EFI system, your car is no different than any other mid '80's Mopar 318, so reasons 2 through 5 are still possibilities for you.

Addition from Bob:

I would like to add a few more suggestions for the spark knock problem you're having. Those that Dick suggested are valid, but add these too:

The Air Flow Sensor only measures induction air entering the Air Cleaner ; You would be advised, on a car of this age, to look at all of the sources of vacuum leakage entering under the Air Cleaner. A quick method is to disconnect all of the small vacuum hoses on the "tree" behind the HSP and cap them closed. Only the PCV Valve and Brake Booster will remain open since they're entering via the Throttle Body. The Throttle Body and Hydraulic Support Plate gaskets are also potential leaks.

Adjust timing to specs and drive the car. If the problem is gone, reattach each vacuum operated device until the rattle returns. If none of these are at fault, suspect the larger gaskets mentioned above, a leaking hose or case at the Brake Booster, or a dirty PCV Valve could be a reason.

Reasons for no knocking upon acceleration is that the computer defaults to open loop which gives the richer mixture needed; at steady running, the mixture is managed to be as lean as possible for clean exhaust, good mileage and reasonable response and so more apt to knock if there is a leakage.

Another common device that leaks is the Vacuum Solenoid switch which has small hoses attached to it for the Purge Canister and Diverter Valve on the Smog Pump. The switch may leak or the hoses may be bad.

Question from Peter (1981):

I have a question concerning the proper spark plugs to use for the 1981 Imperial with EFI and 318 engine. The plugs that I removed from the car were Champion RN14YL with a gap of .045. These plugs are no longer available and the one which are close are RN13YLC. Would these plugs be ok to use and what is the proper plug gap. The car has 54,000 miles on it and I presume that the plugs were never changed. I have another question that maybe someone can answer. When I got the car it would start ok when cold but was hard to start after it had been run for a while and after a short shut down period. When it started the idle would seem to be trying to find itself fluctuating up and down quite a bit. The Hydraulic Support Plate power module and the fuel flow meter had the potting melted. I ordered a new HSP and installed it. When I went to start the car the fuel would continually flow from the injector bars. I do have the service manual and followed the steps to find the cause. It turned out to be the Combustion Control Computer. I replaced it with a used one that I picked up for a spare and the car has run fine ever since. That would be for the last 5,000 miles. It is now in storage for the winter. Is it possible for the Computer to go bad that fast or was something else to blame. IT never had the fuel flow problem till I changed the HSP. The car starts and runs great including the idle.


From Chris:

I don't know which plug number your Imperial uses, but allow me to start (and hopefully end) the thread of endorsements for Autolite plugs instead of Champions. They are all I will use in my Mopars, and a huge number of people on this list will agree. The Autolites tend not to foul and they cure pinging.

Good luck... you will be happier with the Autolites!

From Dick:

You've had a common experience with these cars - the potting compound makes a mess in all of these cars sooner or later, but it does not seem to cause any operational problem, other than occasionally interfering with the throttle butterflies, making the accelerator pedal hard to push. The goop dissolves in Acetone or in Lacquer thinner, but it is really sticky stuff, even when somewhat diluted.

The variation in idle speed is present to some extent in all these cars, as there is a constant monitoring and adjustment of idle speed going on all the time when the car is idling. Some cars hunt up and down by 100 RPM or more, others seem to keep it in a 50 RPM total range. The main variable seems to be the amount of wear on the linkage from the automatic idle speed motor to the throttle shaft bellcrank. I suppose when mine gets bad enough to warrant it, I will pull the parts off and make new linkage parts to tighten things back up again. At 120,000 miles, mine is still fairly mild in it's hunting behavior.

I have run the Champion RN13YLC plugs in my cars, or the Autolite 945's, which are just about equivalent to the original 68ERs specified on your tune-up information. They seem fine. There is confusion about the spark plug gap, and a service note on this in the TSB's (available at The consensus seems to be that idle is improved if the gap is set at 0.035", and that is what I have done.

Your warm restart problem was probably caused by an out of spec fuel pressure switch. We recently found a modern replacement part for this, which you will find by doing a search of our IML archives. I hope you saved your old HSP and CCCs, these are scarcer than hen's teeth these days, and the dealers are not much help.

The symptom of constantly flow fuel from the fuel rails is usually caused by a failure in the power module, but yours seems to have been the CCC. I'd keep all the old parts, some can be repaired if necessary, and often what was thought to be a bad part turns out to be some other problem, for instance poor ground on the ASDM, or loose connector, etc.

You probably already know this, but it cannot be emphasized too strongly that you MUST keep the air cleaner lid on tight and well sealed, and prevent any air from entering the intake without passing through the air flow sensor. This one problem has turned out to be probably 80% of the operational problems with these cars.

Your mpg and performance is just about in perfect agreement with the others of us who enjoy these cars. Welcome to the group, and brace yourself for an onslaught of people trying to convince you to give up on the EFI and convert it to carburetor (UGH!).

From Bob:

The correct Spark Plugs for this car are Champion RN14LY; the gap was changed from 0.048" to 0.035" via Tech Service Bulletin No. 08-14-81.

Question from Stan (1981):

If the Champion plug were available what would i want to put in the car RN14YC or should I look for RN12YC?


From Bob:

The correct plugs for the '81 and '82 EFI Imperials are Champion RN14LY, or MoPar 68 ER, a Champion plug, as original equipment, (we went over this a couple years ago). The TSB 08-14-81 revised the gap, (which was: 0.048" down to 0.035" ), for some cars with "Driveability" problems during Warm-Up. For cars without these problems, the original gap was fine - advantages especially for lean mixtures at speed. For '81 and '82 318 engines with 2BBL carb, the original plugs were MoPar 65PR or champion RN12Y. Chrysler later recommended all plugs for these cars have a reduced gap. The "L" symbol would be voided when the gap is reduced down to 0.035." All this without a part number change. I still use the wider gapped RN14LY. 0.048," and they are fine. They burn clean and the gap does not erode at a fast rate. The basic idea was sound.

From Dick:

If you prefer Champions (most prefer other brands), you would need to specify RN13LYC. The plugs you mentioned are perhaps correct for non EFI cars, I'm not sure. But for an EFI car, you want the "L" in there (it specifies the extended gap plug). The original plug, the Autolite/Mopar 68ER is no longer available, so you need to find the closest equivalent. The Autolite 945 is very close, but these are getting hard to find also.

And don't follow your manual as to gap- the correct gap is 0.035".

Question from William (1981):

I am ready to change out the plugs on my '83 EFI. I bought RN12YC Champions to put in it (that is what it says in my FSM and on the radiator support), but I found on that someone recommended RN14LY plugs. Should I ditch the RN12YC's and go with the 14YL? What is the difference? I am not looking to open up a debate of which brand is better, I have my reasons for using Champs, I just want to get the best one. Any suggestions on gapping? 0.048?


From Dick:

I have always used RN13LYC (don't forget the L!), or Autolite 945s. These are the closest to the original 68ER plugs, which are no longer available. The Autolites are getting very scarce also.

The correct gap is 0.035", not the 0.048" given in the manual. I don't understand how the core support label could recommend RN12YC - I don't think that would be correct for any of these cars, except possibly the carburetor converted ones. The core support label on all the EFI cars I have seen recommend the 68ER.

These cars like to be driven. As you know from reading your engine performance manual, the computer "learns" your driving and engine conditions with use, and keeps the car close to optimum more of the time, the more you drive it.

From Neil:

If you can't get the Champions why not use the Autolite 945's?

I wouldn't carry Champion's in my trunk let alone rely on them, they are the only manufacturer of plug that i have found bad from brand new on many occasions.

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