Hey everyone, first time poster... long time lurker. I always use these forums to help with problems I'm having but this is the first one to stump me so I am seeking help from the guru's on the site.

Here is the truck: 97 GMC Sierra 1500. 5.7L, 4x4, 166,500 miles.

Here is the issue: I am having a very intermittent problem with my truck starting. Within the past 6 months I have replaced the fuel pump, oil pressure switch, and fuel relay. I also have a Clifford Matrix remote start/alarm that I have disconnected because I have heard those can cause problems with starting. The problem I'm having is sometimes the fuel pump will prime and the truck will start and run just fine.... and then 2 seconds later I'll try to start it and the fuel pump will never prime. I'll leave it over night, not moving or touching anything on the truck and it will start just fine. And then I'll shut it off, try to start it and it won't. Now, it won't start at all... it just turns over. I'm getting good spark and I know the engine runs fine, I sprayed a bunch of starter fluid into the intake and the truck will run for 10 seconds or so and sound completely normal.

So after speaking with a mechanic he said it could be a couple things: bad ground wires, pinched/frayed wires, or a bad ECM. I called Chevy today and they said they have to have the whole vehicle there in order to check the ECM. So I'll start with the simpler things first, cleaning ground wires and what not.

After writing this short novel (sorry, I just wanted to give you guys a full background so it's easier to diagnose) I just need some help with the troubleshooting parts... IE: where are the ground wires I should clean and what's the best cleaning solution? (baking soda and water? maybe use a wire wheel or hand file) Also, how can I check voltage to be sure the wires that power the fuel pump relay or getting what they are supposed to? Anything you guys would do first when checking the "smaller" things before I start replacing anymore parts and spending bookoo bucks.

Thank you everyone... I really appreciate the info and help!!!

 

I forgot to mention as well, I have a Superchips Power Programmer that had the "Performance" map installed. I took that map out and installed the "Stock" map just to be sure. Also, my ABS light is "On" and every now and again I get a "Check Engine" light. So far, everytime I've gotten the Check Engine Light it's an o2 sensor so I just clear the DTC. Those are the only known problems I can think of at the moment.

 

Bueler, Bueler...... anyone, Bueler?

 

Come on people... I really could use some help. I've tried searching these forums for days trying to find something, but I can't find anything. Please help. Thank you.

 

Im not an expert, but I do know that with electronic fuel pumps you should hear them building pressure when you turn the key forward, not all the way to start, just to where you get accessories (i dont know if this works when you turn the key full back to accessories) but you should here the pump under the vehicle "throbing" or pumping. Which just maintains good pressure and any extra is returned. I would make sure you have that to start with.

Also, I am not very experienced with the more computerized systems, but I would try disconnecting the battery and reconnecting it...

 

Seems like a bad ground or wires. Best thing I could say is just trace the wires from the fuel pump. I've never had to trace those wires, can't really say where they go.

 

Did u have this problem before you replaced the fuel pump? What brand pump did you put back in it? If you cant find any bad or broken grounds i would suspect the fuel pump is bad, even tho you just replaced it. I would put whatever brand fuel pump came out back in I.E. Delphi, delco, because the cheaper ones are known to go out very fast sometimes. Keep us posted please, and welcome to the forum!

 

No, this problem did not exist before replacing the pump. And I put in a "Bosch" pump... which was actually MORE expensive than the Delphi that was in it to begin with. I know it wasn't the wires coming FROM the pump because my brother and I just went ahead and took the entire bed off of the truck to replace the pump. (It was actually easier to take the bed off than take the tank down) I know there is a way to "hot wire" the fuel pump under the hood to check if it works, but I do not know which wire to tough to my positive termial... does anyone know?

 

Taking the bed off this weekend again to see if it's the pump, wish me luck.

 

the bypass wire of which you speak in located in the wire bundle near the master cylinder near the fuse panel....
apply 12v to the connector and the pump should come on