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Edward, ASE Certified Technician
Category: Ford
Satisfied Customers: 2747
Experience:  ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000
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Ford F150: I have a 1992 Ford f150 with 5.8L efi and two fuel

Customer Question

I have a 1992 Ford f150 with 5.8L efi and two fuel tanks. Problem when key on engine off fuel pump does not shut off check engine light on. It will start but flooding bad. Changed fuel pressure regulator, fuel filter, checked fuel pump relay, complete tune-up.
Submitted: 5 months ago.
Category: Ford
Expert:  Edward replied 5 months ago.
Hello, So I'm clear, The pump doesn't run all the time, but when you turn the key ON, the pump continues to run without even cranking the engine? thanks.
Customer: replied 5 months ago.
Right. In the koeo position pump runs. There is a pump in each tank right? They both run with key on.
Expert:  Edward replied 5 months ago.
I'm 95% sure there is a lift pump in each tank, but the high pressure pump is on the fuel rail on drivers side on that model. I'd have to check it to be sure, but I believe you will see a high pressure pump on the fuel rail drivers side about under your seat. Is this the original PCM (Engine Computer) in the truck. the PCM grounds the Fuel Pump Relay, and is responsible for cutting off the ground to the pump after initial 2-3 second prime when you turn the key on.
Customer: replied 5 months ago.
Yes I believe it is the original PCM.
Expert:  Edward replied 5 months ago.
Alright, I actually show two high pressure pumps in the tanks on that model. No lift pumps and 1 high pressure pump no the rail like I thought, that was late 80's that had that, and 460 engine in heavier trucks had it as well. So I don't think you have the pump on the rail.
Customer: replied 5 months ago.
So what would cause the pumps to run continuously?
Customer: replied 5 months ago.
What do I need to fix?
Expert:  Edward replied 5 months ago.
There is a LIGHTBLUE/ORANGE wire that comes from the PCM to the fuel pump relay. If you unplug the relay, and check that wire with an volt meter with key on black lead on BLUE/ORANGE and red lead on positive battery cable, if it shows constant 12 volts, then the PCM is either grounding the relay constantly and you need a new PCM, or the wire is shorted to ground somewhere between the relay and the PCM. which I kind of doubt. I would try another PCM if BLUE/ORANGE at the fuel pump relay has a constant ground on it with key ON. it should ground for 3 seconds only, That should fix it barring any wiring harness shorts. Let me know if you have any further questions.
Expert:  Edward replied 5 months ago.
I have seen this problem before and a PCM fixed the fuel pump that didn't shut off with the key on.
Customer: replied 5 months ago.
Thanks Edward. In
Expert:  Edward replied 5 months ago.
Absolutely, Thank you.