My 2004 Z06 died pulling into my driveway today. Fuel pump is not running. I don't hear any fuel pump whine when i turn the key on. Check fuel pump fuse (20 amp) looks good. Replaced fuel pump relay (#35) didn't help. Get a small amount of fuel out of the fuel rail with the key on.

Im not too familiar with where to start. Any help is appreciated.

 

Check for power at the pump connection while someone turns the key, if you have power there for the few seconds without any pump action you might as well buy one and change it out. Not that bad a job once you drain the tank.

 

Thanks for the tip. I can get to the pump plug of an 2004 by removing the wheel well liner to test if its getting power?

Can you replace the fuel pump without dropping the subframe in a 2004? I thought it was a royal pain, at the top of the tank or something?

 

You have to find out why the fuel pump is not running. The PCM controls the relay that powers the fuel pump, so as mentioned previously check for power at the fuel pump and determine if there is or is not power at the fuel pump.

 

.....and ground....

 

Do you have a 12 volt test light ??…if so we can show you how to test the relay.

 

I got to the fuel pump plug and disconnected it. i attached multimeter and had my son turn the key. wasn't sure which of the 4 prongs to be on, but on the first two i got 12v and on the other 5v. so im assuming thats 12v to the pump and 5v for the fuel gauge? Either way, looks like im getting voltage to the fuel pump?

 

I don't but i could get one. but see my post above.

Does this mean i need a fuel pump?

 

Is it possible that no spark could shut down the fuel pump?

 

If you lose the crankshaft position sensor signal and have no RPM input into the PCM the engine will shut down…the pump will however run for 2 seconds and shut off without this signal.

 

that makes sense. What stops the pump after 2-3 seconds of ignition on?

Car only has 33k miles. I know the pump is 20 years old but i want to do everything i can first ofc.

 

Just because you see 12 volts on the power side doesn’t mean it’s good…the best way to see if you have the proper CURRENT going to the pump is to do a voltage drop check from battery positive to the fuel pump power feed wire…this should also be done on the ground side…say if you have a drop of 5 volts that means only 7 volts is getting to the pump… current follows voltage so you would have less current going to the pump too…your pump draws about 6 amps or so…now if you had a bad ground that current can also be low on the ground side…many DIY’s don’t understand what the ground circuit does…they only think they hook up their DVOM to a ground to read battery voltage. !!…if I’m checking a C5 pump that is not working I will substitute a “load” like a headlight bulb that draws 5 amps…if I hook it up between the pump power and ground connector terminals and it’s bright I know the circuit is fine…if the light is dim I know have to determine which side of the circuit is causing the drop in current…I just helped someone on the C6 Forum with a pump issue and his problem was a burnt terminal on one of the connectors going down to the pump… if you have a paper clip bend it into a U and jumper the load side of the relay and see if it runs…it’s terminals 30 and 87…picture below…if the pump runs your issue is on the “control” side of the relay.

 

The software built into the PCM…video below !!…the coil feed is power side switched so if you use a DVOM to check that terminal you will see 12 volts on it at all times…that is why we use a test light and when we hook it to ground the test light will illuminate for 2 seconds and go out.

 

So - two things. 1) To answer your question - The PCM operates the fuel pump relay for about 2 sec when the ignition is first turned on. Then the PCM opens the relay unless it "sees" the engine turning...

2) I believe that sometime in the 2003 Model year - the fuel pump access got substantially worse. The earlier C5's had fuel pumps that could be accessed without removing the tank - I believe late 2003 and 2004 cars require the tank to be dropped to get the fuel pump out.


So - if I were you I'd listen very carefully, and turn the ignition on - you should be able to hear the pump run for a couple of seconds. If not - you can always try pulling out the relay and jumping power directly to the appropriate terminals (see attached file w pic). If the fuel pump is operational - that WILL run the fuel pump.

 

 

If i jump 30 and 87 the pump runs!
If you could help me diagnose I would be very grateful! Im very lame when it comes to electrical, so any step by step would be much appreciated!

 

Are you saying you jumped 30 and 87 and it runs ??…don’t worry I’ve seen 20 year professional mechanics who couldn’t diagnose this circuit !!

 

the fuel was spraying out the schrader valve with 30 and 87 jumped and key on

 

Ok, great so we know the load side is good…we need to test terminals 85 which is the PCM controlled side power and 86 which is the coil ground…best to use a test light for this…I use a test light more than a DVOM…as mentioned in the video using a voltmeter on terminal 85 will mess you up !!…this headlight bulb is what I’d use as a substitute “load” to check the power and grounds if the pump is inop to check wiring integrity.

 

can i jump 30 and 87 and make the car runs/starts quick?

i'll watch the video, but should i go ahead and clean grounds? what will the test light tell me? i don't have one so i guess i'll buy a test light?