Hi there,

 

The probelm is that when i key the car over i get 11 volts at the pump but then suddenly it drops off to 0 vlots in a matter of like 2 seconds. The pump never comes up adn i wonder if it is shot.


Any help is appreciated

sparrow

 

What do you mean "the pump never comes up?"

Try placing 12v+ to the "G" terminal on the ALDL. Thats the bottom left hand port. Do a search, the ALDL port diagram has been posted hundreds of times. Anyway, the "G" port is the fuel pump test port. It places 12v+ directly to the pump, bypassing the fuel pump relay. If the pump is or there is a bad wire somewhere, the same thing will happen (power for 2 seconds, then drop off) when powered via the ALDL. But to me, it sounds like the pump is priming and then shutting off.

 

The ECM grounds the fuel pump relay for a few seconds at power up to pressurize the rail. The ECM then turns the FP off. Once the engine builds sufficient oil pressure (starts), the oil pressure switch, above the oil filter, will close and power the fuel pump.

 

So everytime you turn the key off and back to run, the pump dosen't prime everytime? It runs off of oil pressure after the prime?

 

The ECM does not ground the fuel pump relay. The coil in the relay (activates the relay's switch when energized), has a GRN/WHT wire and BLK/WHT wire. The GRN/WHT wire goes to the ECM and the BLK/WHT wire is tied into the engine harness ground. The ECM energizes the relay's coil by sending 12v through the GRN/WHT wire. Also, the motor will run without the oil pressure switch. The oil pressure switch does not take over. However, if the fuel pump relay fails, the oil pressure switch will "take over".

The electric fan relay is just the opposite. The coil in the relay has a BRN wire and a GRN/WHT wire. The BRN wire goes to an ignition power source and the GRN/WHT wire goes to the ECM. The ECM grounds the relay's coil when the specified temperature is reached.

 

The fuel pump does not always prime every time you turn the key to on.

The pump does not run off of oil pressure after the prime. If you look at the wiring diagrams, the pump runs off the relay and the oil pressure switch. If the relay fails, the oil pressure switch will keep the pump running. In fact, you can probably start the engine without the fuel pump relay, but it might have to crank a little longer to build oil pressure before the oil pressure switch closes to energize the fuel pump. You can definitely run the fuel pump with the oil pressure switch disconnected...as long as the fuel pump relay is good.

 

Thanks for the reply S10. The problem I'm having is when cold the pump will prime and it will start right up. When warm, it will not prime and may or may not start after some cranking. I've noticed lately that the pump will prime, after extended cranking, when I let OFF of the key. Now, to get it to start, I quickly bump the starter, let off of the key, get primed and it fires right up. Don't know what to check next.