1999 Suburban 5.7 crank no start

Joseph Bowden · July 30, 2019

I have a 99 GMC suburban, 5.7L 4wd, it's not getting fuel. the pump works, sender is good, FP relay is good, and all the wiring in between. The problem is the ECM / PCM / VCM is not energizing the FP relay. I checked this at the module, and there is no control signal to the relay at key-on. However, if I jump the pump and start the engine the pump runs fine. Kinda Sounds like a bad ECM, but I'd like to know, is there any other input (or lack of one) to the ECM that will cause it to not energize the relay?

riverbanks · July 30, 2019

Are all fuses good?

Joseph Bowden · July 30, 2019

33 minutes ago, riverbanks said:

Are all fuses good?

Yep, all under-hood and driver-side fuses are good according to my test-light.

riverbanks · July 30, 2019

Did you check pcm connection?

Joseph Bowden · July 31, 2019

Meaning what exactly? the green/white wire that goes from PCM to FP relay and energizes the relay switch is in PCM connector C4 I believe (which ever one is labeled "black"). All the terminals in that connector are nice and clean. In fact, almost all the terminals are surprisingly clean, except the fuse terminals which are all kinda brownish. Not damaged, just brown.

riverbanks · July 31, 2019

Meaning that, exactly,lol,darn,this is rare,right,it runs fine when jumped,for just one circuit to go down,do you think it's worth putting on a scanner,and commanding the pump on?

Joseph Bowden · July 31, 2019

It belongs to my boss, so that would be up to him. I assume the purpose behind that would be to see if the PCM is capable of energizing the relay?

riverbanks · July 31, 2019

Yes,I did just scour the internet,found 1 that a new pcm fixed it,on CarGurus site

Joseph Bowden · July 31, 2019

Thanks. my scouring was fruitless XD

either it'll get replaced, or I'll wire in a manual switch.

Joseph Bowden · August 2, 2019

So I forgot to mention the problem is intermittent. Well, more like it intermittently doesn't have the problem XD

Anyways, during no-start the gauge is pegged out way past full. For a while, you could let it sit for several minutes and all the sudden the gauge would come alive and read right, and then you could start it. After the gauge comes alive, if you turn the key off and wait for 5 seconds before turning it back on, the problem comes back. If you turn the key back on within 5 seconds there's no issue. Today I cut out the crappily installed butt-splices in the 4 wires at the fuel pump/sender and installed new ones properly. The problem is less now, in that it usually only takes a few seconds instead of minutes before the gauge comes to life. I was able to scan it and it had a code for high voltage on fuel level circuit. Cleared it and it hasn't come back, so im assuming its from my buddy connecting random wires up trying to fix it. The fact that putting in good connections made the problem so much better makes me wonder if I should just re-wire the fuel level sender.