Alright, so here is my very frustrating story that will hopefully make some kind of sense to you.

My 89 IROC with a 91 350 and Z28 guts had been running, and running better than it had for a long time. Then, I parked it one night it rained an absolute **** ton. Went to start my car the next day, wouldn't start. I knew immediately fuel delivery of some kind was the problem because the pump would not prime, which with my car you would always hear. So I figured that it was probably the relay. Tested my relay every way I could think to test a relay, continuity, voltage, switching...Tested out fine. So i figured my fuel pump had kicked. Just finished pulling the pump, hit it with 12 volts and it fired right up. I am damn near out of ideas. The only other thing I could think to check is for shorts in the wiring.

Help guys!!!!

 

You have corrosion on a connection. Not likely the computer connection, most likely at either the relay or at the connector between the tank and the body at the rear seatback. When dry, the connection just barely passes enough current to run the pump, but the dampness exposes the fault.

 

Alright I will definitely look into that and report back. Thanks

 

Cleaned everything up and it didn't solve anything. I can get voltage at the connector behind the seat all the way down the sending unit to the pump, but the pump won't run. I don't know if there's not enough current behind the voltage or what. Once again, my pump is good, when hit with seemingly any voltage other than what my car is supplying, the pump runs. When I jump across the fuel pump relay coil, the pump still won't run. When I jump the oil pressure switch, my pump still won't run.

Any more ideas?

 

Does anyone have any idea of the kind of route taken by the hot wire, ground wire, and fuel gage wire to get from the engine compartment to the connector by the fuel tank?

 

So, when you put 12v and ground on the pump from an external source, it runs. The car is supplying 12v to the gray wire in the fuel pump harness.

Is the car giving the pump a good ground on the black wire?

 

Isn't there a fuel pump factory prime wire on these cars? Might hit it with 12v direct from the battery. Eliminate a wiring problem from front to pump.