Ok I got this car about 2 weeks ago that had a fuel pump issue. The pump wasn't getting power. I took out the pump and replaced it but found the wires going to the pump were burned up. I got a new sending unit from a real good member here (gvincent) who shipped it up perfect and sent it fast for cheap! But I put that in and nothing. Here is what I have replaced so far:
-the 15 watt fuse
-the relay up on the driver side floor panel
-the fuel filter
-the fuel pump
-the entire fuel sending unit

I have used the grey wire jumper and that worked no problem....we got the car running but as soon as we took the wire off the jumper, it died obviously. I could rig up a wire w/ a switch...but I want to fix this the right way

Best I can tell, if the relay works, but the pump isn't getting power...it has to be in this section of wire here:

(This isn't the car, but I just had the interior outta my other 94 camaro so this picture has showed me where the wires are!)

Is there something I am missing or does the problem have to lye in this stretch of wire? Also where is this fuel pump ground that gives everyone problems? If the fuel pump jumper works, the ground should be fine.
I searched all the way back to 2003 and couldn't find any topics w/ the fuel pump like this....anyone have ideas?
I am taking the interior out tomorrow but figured I would run it by my fellow cz28 friends and see if I am missing something obvious!
Thanks to any/all in advance!

 

So does jumpering 12v to the prime connector under the hood run the pump? This is a 1994?

 

Yes jumpering it runs the pump, and this is a 94 z28 M6....have any ideas? I would have just emailed you but figured someone may have this issue in the future.
Thanks

 

Then you don't have a wiring problem in the area you highlighted in the pic. The power has to go through all that to get to the pump.

Are you really sure the relay is operating when you turn the key on? Replacing the relay does not mean it is working.

 

I am positive the relay is still working. You hear it click after about 2 seconds...I also just got a new one as a way to rule it out. Both the old and new relays don't let the car start..and both of them make the clicking sound.
What else could it be?
Thanks Shoebox

 

Look at the fuel pump wiring diagram on Shoeboxes Tech pages (pcm3):

http://shbox.com/1/4th_gen_tech2.html#1995_pcm_wiring

The gray wire from the fuel pump prime connector meets the fuel pump circuit immediately after the circuit comes off pin 87 of the relay. If your relay is working, unplug the PCM "A" connector to prevent any voltage reaching the PCM while working in the circuit. Turn the key to "on". Apply +12V to the 85 pin of the relay (dk green/white wire). If the relay is working, you should have +12V at pin 87, and at the fuel pump prime connector. If you don't have it there, the break is somewhere in the wire between pin 87 and the point where the prime wire connects. That is the only possibility, assuming the relay is good and the piece that the relay plugs into isn't damaged.

 

Ok I finally got a chance to look at this problem, and here is what I have come up with:

The relay circuit is functioning properly. With the ignition ON there is +12V going to the coil on the relay. After reinstalling the relay I verified it was working properly, (12V output when coil is energized) and it was. I then checked for voltage at the connector next to the fuel pump (Black, Purple, and Gray, connector is located right behind the drivers side rear passenger seat). There was only ~+7V across the purple and black pins on the connector (These are the +V and ground wires for the fuel pump) This leads me to believe there is a 4-5V drop between the relay and that connector. I am waiting for Josh to get home so we can take the carpet up and find out whats wrong.

My hypothesis:
When Josh first started working on this car, we assumed it was a bad fuel pump. When we pulled the old fuel pump the connectors going to the fuel pump inside the tank were melted



This leads me to believe the old pump seized up at one point in time, causing the wires to get too hot and melt. I am thinking somewhere between the connector behind the backseat and the relay, there is a wire that is probably melted a little and is making contact with the body or another wire, causing the 4-5V drop.

 

Well I was right. I pulled up the carpet, unwrapped all the wiring going to that connector behind the backseat, and it started right up. There is either a short or a broken wire somewhere, I am working on finding it right now. Will post pics when I find it.

 

Well I found the problem. I noticed if I help the fuel pump relay a certain way it would work, and if I put it in its holder it wouldnt work. Here is the culprit. The jackass who had the car before had all these blue lights hooked up in random places. I guess he decided to use these wires, and when he unhooked it look what he did to reconnect them:


Idiot, people that do stuff like this **** me off

 

Thanks to Captain I got the car running...the harness going to the relay seems to have a loose wire or pin. Captain pulled the wires back and zip-tied it and it has been working, but it needs replaced....anyone have a junk 4th gen w/ some wires to get rid of?
Thanks again Shoebox

 

I am having the same problem......replaced relay and then one day i had the panel off by my feet and could hear the relay clicking over and over for some reason like there was a wiring problem somewhere.....already replaced the relay and that will make it start right up but then give it some time and forget it. Will be looking under the car this week as im still working on mine. Will let you know what i find....having it not start is really annoying.....