Thread: Troubleshooting fuel system issues.

Hi all,

With the key in the "on" position, I have 11.8 volts at the 3 wire lead to the fuel pump but no voltage at the two wire lead. Any ideas where I should start. My fuel pump doesn't make a whir sound anymore when I turn the key.

So I jumped the relay and the pump is working but I'd expect my car to start now. Is there something about jumping the relay that would prevent the car from starting?

Also, I just swapped I the ac relay in place of the fuel pump relay and the fuel pump doesn't start. Anyone have any guesses why I can pump fuel with the relay jumped but not with a relay in place? My ac relay should be good.

Check fuel pump fuse. If that's good, pull the relay box cover in the engine bay (near the battery) that has the (probably green) fuel pump relay, take off the top of it and grab some 18-gauge wiring and bridge a connection between the bottom and top right pins to the positive battery terminal (be careful and don't get shocked) - The fuel pump should prime immediately even w/o the key in the ignition. If it doesn't, it's the pump. It if does, suspect the relay at the ECU.

Fuel pump definitely primes and I have fuel at the rail with the jumper in place. Going to check spark and compression. After that it has to be air or ecu/electronic issues.

The contacts inside the relay are probably dirty, (it happened with my horn relay)
use a 9v battery to activate the relay and use a ohm meter to test the resistance across the high current side of the relay. It should be close to Zero as possible.

When i checked my horn relay it was around 100ohms and that was enough the horn wouldnt blow. I cleaned the contacts and put it back in, and it worked.

I had never heard of that trick but now I'm stealing. Great advice.

So I haven't "cleaned" the relay yet but I did swap in my ac relay which I know works and still the fuel pump only works with the jumper. I assume tha means the ecu isn't signaling correctly. Anyone have any good ideas where to look next?

test the signal wire from ECU to the relay... might be broken