So my husband has been working on a 2002 Sonoma for a friend; she told us the fuel pump was going bad, so he had replaced it. Here we are 2 months later, and she says she has trouble starting it, sometimes has to bleed the fuel line to make it start. So we start looking into it further and cannot figure it out. We discovered that the fuel pump relay was corroded, so we changed it. Still won't start. Worried the new fuel pump was bad, he disconnected it from the wiring harness and wired it to an auxiliary battery and it starts just fine, hook it back to the wiring harness and it wont start. Hook a test light up to the wiring harness/fuel pump connector and its getting power. And ideas? Worried its a wiring problem, but not sure which end to start at or if there is something else that could be affecting it?

Thanks!

Need to check the ground side of the fuel pump harness to see if it has good connection where it attaches to the frame.

As Will has said, run a separate ground wire straight from the battery to the fuel pump. I had a similar issue with my 2000 Blazer which shares a common wiring system as your Sonoma.

I had the same problem on my Son'* S10. It was a frayed ground wire. would make a connection at times, not at other times.

The good news is this is fairly easy to inspect and does not require removing the fuel pump. The ground for the fuel pump is located in the far rear of the bed on the drivers side. The fuel pump shares the same ground location at the frame as the rear tail lights (not the same ground wire though).

Near the drivers side rear of the bed, you will see some wires from the tailights bolt to the frame. You will also see on wire from forward of the frame. This is the fuel pump ground. Good chance you will find nicks in it, somewhat common. The diagnostic and fix is under 30 minutes. all done with normal tools.

I thank you guys for your help, he replaced the ground wire and the truck started right up 4 times in a row... went back to it an hour later, and it won't start again. This is starting to drive us mad, if anyone has any other suggestions we would really appreciate it!

Thank you,
Amy

Working on a 2002 GMC Sonoma

sounds more like the pressure regulator or poppet issues they have. you should get a pressure gauge and see what the pressure is and if the pressure stays

We had the same thought, and the pressure starts out good, but it is dropping as it sits, slowly but it is dropping. It starts most times now though, since he reran the ground wire (thank you all again), so my friend being a poor college student said she will just take it as is for now and try to sell it rather than dump more time and money into it, shes had nothing but trouble with it since she bought it last year. I thank you all for your help, its great when you can find a forum with nice and helpful people on it! (and when you agree with what I tried to tell my husband all along, but most of you guys have a hard time listening when it'* a girl talking, lol)

Sincerely,
Happy to have this truck outta my driveway!
Amy

Wait, you were a girl all this time?!! I never even knew. I think I've been Rick Rolled.

Thanks for stopping by Amy, and your more than welcome to stop back in and pester us any time.

The other issue with the S10/ Sonoma/ Blazer/ Jimmy/ Bravada that simulates a failing fuel pump is the ignition switch. It is located in the steering column. Not to tough to replace, you will need a mini torx set to remove and replace. Be careful not to damage the hazard indicator while removing the steering column cover- it is easy to break and it will reuslt in the replacement of the turn signal multi-function switch (don't ask how I know this).

So, we convinced the owner to let us look at the fuel pressure regulator. Hubby tore into the injector head, located the regulator... and it'* not hooked up to a vacuum line, and there isn't a loose vacuum line to be found? Doesn't seem right to me? Husband says there just isn't one... so, anyhow, should we try replacing the regulator? The fuel pressure drops slowly when it sits, and one side of this regulator doesn't seem to hold pressure...