Hey Ferm

[THEFERMANATOR]

On a 94 the fuel pump runs either by the oil pressure switch once the engine is running, or by the relay which is triggerred by the ignition switch start circuit. The oil pressure switches are a known issue for 95 and older GM diesels as they run the entire fuel pump load through the oil pressure switch and burn out pretty often. Most wire them to run all the time when the key is on, or install a relay inline to carry the load and use the oil pressure switch to trigger the relay. If the pump works when you hit the key, but you don't get fuel while it is running then most likely your oil pressure switch is bad. Only use an ACDELCO replacement as the aftermarkets will cause you to pull your hair out. No fuel presssure while running can cause all kinds of problems, and also take out your injection pump.