Cadillac: Fuel shortage problem, oil pressure switch, fuel pump relay

Question
I have a 1991 Elderado Touring Sedan and it has been idle for 5+ years with a dead batery. I replace the batery and put fuel in the tank and put on a new fuel filter I than tried to re-start it with no success. I have come up with a slight problem. The fuel pump wants to only run for 2-3 sec and than it won't run any more for a while, the car will run if I pour fuel into the throdle body, but it won't pick up the fuel to keep running. Got any Idea what I can do to fix this short of having the computer re-flashed to fix this problem.

Answer
Fuel pump test:

1. Get yourself a helper.

2. remove the gas cap.

3. have one person listen in the gas tank at the gas cap opening.

4. have the other person turn the ignition switch to the ON position ONLY so as the dash lights come on. Do NOT attempt to start the engine.

5. As soon as the ignition key is turned to the ON position, The person at the gas tank should hear the fuel pump run for TWO SECONDS and then it should STOP.

6. Does it ?.

7. If it does NOT run for the 2 seconds the fault is either the fuel pump or the fuel pump relay.

8. You need to put a fuel pump gage on the fuel line to be sure your getting sufficient pressure.




As soon as you turn ON the ignition switch to ON position, Just before you turn the key to the start position when the engine starts to crank over, A 2 second battery voltage signal is sent from the computer to the fuel pump relay and then from the relay back to the fuel pump in the fuel tank. This runs the fuel pump for ONLY 2 seconds of which pressurizes the fuel system in preparation to start the engine.

Once the engine starts, The computer BYPASSES the fuel pump relay and  sends constant contionous battery voltage from the computer to the oil pressure switch of which is now CLOSED because the oil pressure is UP because the engine is running. Therefore the battery voltage flows thru the oil pressure switch back to the fuel pump to run the fuel pump constantly until you turn OFF the engine.
Therefore if your POSITIVE you are hearing that 2 second pump run just when you turn the ignition switch to the ON position ONLY, just before you turn the ignition key to the start position, I would have to say  you have a weak fuel pump upon initial start up.
If you are NOT hearing that 2 second fuel pump run, Then I would say that the fuel pump relay is defective.