i am currenty working on a customers 90 f150 with the 300 six when you turn the key on to get the fuel pump to prepressurize the system instead of shutting off after 1-2 seconds the pump could run for up to 15 min befor shutting down all the while the engine wont start and if you wait for the pump to stop the truck runs fine after extensive testing and probing ive found that while the pump is running both wires controling the injectors are 12volts pos but when the pump stops the pulse wire goes nuetral until u turn the engine then it pulses ground as it should i just want to conferm that the ecm is at fault ive checked for sticking relays and shorts but from all my understanding of ford fuel injection the amount of time the fuel pump comes on to pressurize the system is predetermined by the computer and is none ajustible ive tapped into the fuel pump relay turn on wire at the ecm and there is 12v but the time is always different anywhere from 5 seconds to 15 mins before the computer suts it off i would just like a second oppinion before i make my cusomer buy an ecm thanks for your time and all help would be very appriciated

 

have fixed this problem before by replacing the eec/ fuel pump relays, they are side by side underhood, check for corrosion in the connectors, replace the relays as pairs and repair connectors if needed