I have a 1992 f 150 300 6 cylinder. Ran perfectly fine then went to start and engine shook horribly with a bad misfire. Terrible fuel smell. Turn key on and pump will not shut off. Seems like it will not pressurize. Replaced pressure regulator but no change. was wandering if it is a stuck injector or possibly a bad ECM. I would appreciate any input. thanks

 

Pull the PCM. Look for blown, bulging, leaking capacitors.

Fuel pump continuing to run with the key in "RUN" position, engine off, points to failed PCM.

Small possibility the fuel pump relay is stuck open....small possibility.

 

Thank you. I will check that.

 

The computer in these trucks has no way to measure/check the fuel pressure. It just runs the fuel pump for 1 second at power-on to help pressurize the fuel rail for faster start.

The circuit inside the computer is designed so that whenever the computer gets by power, it turns the fuel pump on by default. When the computer has finished starting up and begins to do its thing (only takes <1 second), it turns the fuel pump off.

If the fuel pump never shuts off, it means the computer is not starting up. In this case, it's usually caused by bad capacitors.