i have 90 convertable iroc with a tpi 305, and sometimes when it is sitting in the garage with the keys out of it, just sitting there, you will hear the fuel pump kick on and run for a few seconds. I would imagine it is just a faulty connection some where, but before i pull out the wiring diagrams, i was wondering if anyone else has had a similar problem?


Any help is appriciated

 

Sounds like the fuel pump relay is screwing up. I say inspect the relay. Bypass it, unplug it, something, and see if it continues to randomly kick in. But my money lies on the fuel pump relay needing replacement.

 

I wouldn't lay odds on it being the fuel pump relay. It has to get a signal from the ECM first.

 

Note: assumptions are based on 88' IROC electrical diagrams.
This is true, the ECM would have to be running because it controls the fuel pump relay time delay. the ignition switch would have to be faulty in order for the ECM and fuel pump relay to energies (although this would be an extreme scenerio,) or for the key to be removed while it's still in the engine on position (I've seen this happen once with an older model Chevy,) but the pump cycling would rule that out as the pump shoudn't shutoff as long as it has power.

The ECM fuel pump control does nothing more than increase the supply voltage already present to increase flow, by changing the overall resistance.

The only other possibilities are a short, but a short wouldn't cycle unless something is something physically causing it, and it would have to be a short to 12v, not ground, the other is the Fuel Pump Switch. This is a switch that is operated by oil pressure, it supplies 12v if there is sufficient oil pressure to protect the engine so that it can continue to run after the Fuel Pump Relay has timed out. The Fuel Pump Relay does not supply the fuel pump with continuous power, it's only function is to temporarily power the fuel pump on startup.

Since the Fuel Pump Relay and the Fuel Pump Switch are both powered by the same fuse, removing the relay would eliminate the ignition switch as a possibility, if the pump continues to cycle disconnect the fuel pump switch, (on my 88' it's located above the oil filter) the only thing left is a power short, but I could be wrong, most likely I am, but I hope this helps.