1991 LX Coupe Fuel Pump running continuously

[mach1matt]

Good evening everyone. I’m having a strange issue with my 91 efi 5.0/AOD swapped notch. The fuel pump will run continuously when I turn the engine off, regardless of key position. It doesn’t always do it, just most of the time. If I unhook the battery for 5 or so minutes and hook it back up it will turn off. Sometimes when I shut the door or open it the pump will shut off or turn on. I tried investigating this problem before and noticed the relay under the drivers seat was missing and just had a plastic cap on the plug. The pump will prime though when the key is turned on. I have no clue what year the donor car was that all the parts came out of. I am absolutely baffled on what could be causing this issue. Wiring is not my strong suit, so any help or guidance would be greatly appreciated. Thanks in advance.


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[rkkcobra]

Good evening everyone. I’m having a strange issue with my 91 efi 5.0/AOD swapped notch. The fuel pump will run continuously when I turn the engine off, regardless of key position. It doesn’t always do it, just most of the time. If I unhook the battery for 5 or so minutes and hook it back up it will turn off. Sometimes when I shut the door or open it the pump will shut off or turn on. I tried investigating this problem before and noticed the relay under the drivers seat was missing and just had a plastic cap on the plug. The pump will prime though when the key is turned on. I have no clue what year the donor car was that all the parts came out of. I am absolutely baffled on what could be causing this issue. Wiring is not my strong suit, so any help or guidance would be greatly appreciated. Thanks in advance.


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Check the A9L cpu

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[mach1matt]

I believe it has an A9P in it. I’m going to pull it out tomorrow when I have daylight and double check


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[rkkcobra]

Yes, either one...faulty cpu can cause pump to stay on intermittently

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[mach1matt]

How can I determine if it’s faulty?


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[mach1matt]

Well, after messing with the car tonight I pulled the cpu and tried to replicate the problem. It in fact happened regardless of the cpu being connected or not. I found that the fuel pump relay is in the passenger side strut tower area under the maf sensor. That would explain why the relay plug under the seat had the black cap over it I guess. When I grab hold of the relay and twist it and the plug the pump turns on and off. I’m going to peel back the wrap on the harness and check for bare spots and replace the relay if I can find one.


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