Re: Fuel pressure problem
So you say that the fuel pump does NOT run at all with the key on and engine off. I thought that when you turned the key to on the pump should come on period, regardless of a vacuum in the tank. The computer starts the pump until the fuel pressure is up to normal. When the pressure sensor reads the correct pressure the computer stops the pump. Correct? If so could be an issue with the fuel pump sensor or the wiring/connection to it?
If a bad sensor says the pressure is ok at say 10psi you would see:
- turn engine off and immediately restart -> no problem because the pressure never fell
- turn engine off for 15 minutes the pressure drops to say 20psi. You try to start-> pump does not come on because sensor says pressure is ok; engine does not start because actually the pressure is low; you keep cranking and the pressure drops below 10psi and the sensor says to energize the pump. Once the truck is running the engine vibrations keep the sensor, which is a mechanical switch, working correctly.
- turn engine off for a week and the pressure drops below 10psi and when you go to start the engine the sensor allows the pump to start and the engine starts normally
Just a thought. Diagnose by connecting a fuel pressure gauge and prove the pump does not come on when the pressure is low.
I would also check the fuel pump relay. Relays can fail in an intermittent fashion and are easy to replace/check.
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