Fuel Pump Problems Associated With Your 80's Imperial


Imperial Homepage -> Repair -> Fuel -> 1981-1983 -> Acceleration

Question from Bob (1981):


I have been trying to help a friend with her 1981 Imperial. She had a friend replace the fuel pump in the tank.  Now there is no power to the pump. He has checked ballast resistor, shutdown module, and fuses. The ballast resistor is fine, but there is no power there either. I told him to try the shutdown module and still no power at the green wires.  What else could it be?




From Dick:

This has gotta be an easy one, Bob. If he has 12 volts at the fuel pump ballast resistor (both terminals of it with large green wires), then there is power at the pump, or else he has a bad wire or a bad ground at the tank. There is nothing at all tricky about this system, the wire goes from the ballast resistor to the pump, directly, without passing go or collecting $200.

The 12 volts to the ASDM also supplies the Power module, so check to see if there is 12 volts on pin 7 there. If so, there is probably a bad connector in that wire ("Z1 12 DG") to the ASDM and in-tank ballast resistor, just follow it along until you find the problem.

If there is no 12 volts at pin 7 of the Power Module, I suspect the ignition switch wiring or fuse #2, perhaps it is loose in it's socket? Also, check cavity #39 in the bulkhead connector. ALL of these places should show +12 if and only if the key is in the start or run position, If any do not, just trace the wire back to the source. Perhaps one of the fusible links has failed.

From David:


On my 81 next to the three pin connector there is one wire (green), I don't know where it goes but if it's not hooked up the pump won't work. Also a bad ignition switch may cause the problem too.

Question from William (1982):

My '82 Imperial quit on me yesterday. I thought it was because it ran out of gas, as the fuel level was very low. It was idling and quit, just as though someone had turned off the key. I have determined that it is a fuel delivery issue (by the way, I put about 10 gallons of fuel in it, as well as some de-icer, as it is cold here!). I checked the fuel pressure unit at the injector, and it reads 5ohm, so it should be OK. The control pump is getting power and working. I checked for power on both sides of the fuel pump ballast, and it is there, so the ballast is good (reads about 1-2ohm), and power is going to the main pump. I undid the large fuel line to the throttle body (I presume this is the feed) and there was no pressure or fuel flow, even when the engine was cranked. Knowing that there was power going to the pump, I measured the resistance of the pump hot wire to ground, and got almost 5000ohms. This has to be way too high for a pump. The way I see it, this means one of two things; either the pump wiring is bad, most likely a bad ground, or possibly the pump itself is bad. For what it's worth, my ASDM does not have a separate ground, but the case checked ok as grounded with the meter. I am going underneath the car tomorrow to check out some wiring and the pump. Unfortunately, I am severely handicapped by not yet having the FSM for this car (if anyone has one or knows where I can buy one please let me know!!). The imperial club website has been invaluable as my only source of info, but nothing can replace the FSM. Does anyone have any tips, like where the pump gets its ground, or if this is symptomatic of another issue.


From Bob:

You don't seem to mention the In-Tank Fuel Pump except to say that after you disconnect the fuel feed line, and cranked the engine there was no fuel flow in the feed line. Sounds to me like the In-Tank Pump, or filters in the tank or under the seat are blocking the flow. Your high resistance measurement was the feed to the In-Tank Pump - right? The Control Pump can run from the 12 volt battery, nearby. Measure voltage at the pump lead-in connector to verify the feed from the Power Module to the pump. If this is all okay, get to the back of the car.

From Don:

My experience with electric fuel pump leads me to believe you might have fried the fuel pump. On most electric fuel pumps, especially in-tank fuel pumps, the only lubrication is supplied by the fuel going thru the pump. The pumps are high speed and when they loose cooling/lubrication, they hand grenade themselves. 

From Dick:

It seems your in-tank fuel pump has failed, as 5000 Ohms is way too high a reading to ground for the pump. To make sure, you can check this right at the tank fittings, measure from the Dark Green #16 wire on the 3 bullet connector to ground. The gray wire in the group of 3 on the main connector at the tank is the ground wire for the pump, so you can verify that this is solid ground at the same time.

If the resistance is as you measured from the front of the car, you need to obtain a replacement pump. The number is given in the IML archives.

You should familiarize yourself with this resource, but to save you the trouble this time, I've attached below a posting from Bob Harris which will give you the information you need now.

>>The correct In-Tank Fuel Pump For the '81 / '83 EFI Imperials from NAPA is the Airtex number P-74051. It is definitely to be mounted inside the tank on the existing "rack" that the old one was mounted to. The rubber silencer pad should be transferred to the new pump. The new pump is slightly smaller in diameter the the MoPar unit and also a little differently configured, but it's 29 gallon per hour output @ 12 volts, (remember this pump is run at a lower rpm after start-up), is just fine at 12 psi. It is 5 1/4" long and 3 5/8" od, with insulation jacket, and has the correct electrical terminals. It is not configured or protected, by design, for external mounting. You can see this pump at your NAPA shop. This pump is priced at $84.00. There is another pump that some have used that is an external pump and it is number E-8094, but it's output is 45 to 50 gph @ 12 volts and is usually available at various stores; you may have to order it. I prefer the Airtex pump. Under-hood placement for fuel pumps is no longer the preferred location; the avoidance of the vapor lock problem alone is reason enough for this, but there are others. Some folks have carefully cut a panel out of the top of the trunk floor to access this pump, (and the float level indicator), to avoid the hassle of tank drop. Keep at least 6 gal of gas in the tank to maintain a cooling medium for the pump. Hope this helps....Bob Harris <<<

If this isn't your problem, the next thing to check is for fuel blockage at the fuel filters, mounted under the body at the passenger side "A" post. A close replacement is also available at NAPA - be sure to replace the fuel hoses at the same time, as the originals are not rated for use with modern fuels.

As others have pointed out, the two volume set of shop manuals for your car are still available through the dealer, at last report. They also show up on Ebay frequently. You need both manuals.

This page last updated February 22, 2004.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club