Originally Posted by
subford
The PCM relay only supplies power to the coil of the fuel pump relay. It can not turn the fuel pump off and on. It can keep the fuel pump from running if it does not supply power to the coil of the fuel pump relay with the key on. But then nothing else would run either.
A stuck closed Fuel pump relay can keep the fuel pump running with the key off.
A chattering PCM relay, or one that does not make a complete connection can prevent the processor in the computer from starting up. If the processor doesn't start, the fuel pump keeps running.
The relays cost next to nothing, and it's a good place to start rather than dropping $150 on a new computer.