I am a new member and thank you all for being out there helping others. I have a 91 F150 with dual tanks. When I turn the key to run/not start, the fuel pump in the tank selected runs constantly, it doesn't matter which tank is selected. It should build up pressure and shut off until started correct? This is an intermittet propblem. When the pump continually runs, the truck will not start. Starts fine when the pump shuts off after pressure has been met. Changed fuel pressure regulator with no satisfaction. What tells the fuel pump to shut off once proper fuel pressure has been established?

 

Fuel pressure has nothing to do with it turning off, it is a timed event controled oy the Pcm. You may have a fuel pump relay sticking those were known for that problem and will even stay on and kill the battery I would try a new fuel pump relay if that isn't the cause you will have to check the wiring, or you may have a faulty PCM.

 

Thanks for the troubleshooting tip but it still runs contantly after changing the relay. I will look at the wiring next. Any idea what a PCM costs?

 

Are you shure that you changed the right relay there are two relays look identical but are differant One has a basic part # that starts in 12 that is the EEC power relay the other basic part # starts with a 9 I believe 9H467 that is the fuel pump relay.

 

I looked again and there are three slots for relays. Trailer tow, Fuel pump relay and EEC relay in that order. The center one is the one I changed and it did not correct the problem. I called the auto store I bought it from and they checked the part number again and it is a GP Sorensen #MR12. So I beleive I changed the correct one. I have found the computer (PCM) but have not purchased it yet. If there is nothing other than the PCM that controls the fuel pump, I guess I am on my way to the bank. Thanks.

 

Thanks to chucks bp for the information. It turns out the PCM was the cause of my problem.

 

You can test the fuel pump circuit directly from the EEC test connector to see if there are any problems before going to another EEC.
In fact you could disconnect the EEC by unplugging it from it's connector (after removing battery cable) then reconnect the battery and test the pump operation from the test connector.