Need Help 96 vortec won't run

ISRACING · July 28, 2003

Ok guys I'm new here just surfed on to the site so any help is greatly appreciated.

I have a 96 GMC 1500 with a 5.7l engine and it just died! out of nowhere won't run, won't start. I replace the fuel filter every time I change oil, I just replaced the fuel pump, screen, and filter in april. I have spark, if I pour fuel down the TB it will run, the pump kicks on for a few seconds like normal with the key on. I just hooked up a PSI gauge to the schrader valve on the fuel line at the intake and I have about 40-45 psi with the key on, and a pretty solid 40psi when you turn the motor over but it still won't run. What is the drop dead absloute MINIMUM PSI needed to fire the injector? Also if it's not my PSI could it be something else that you might know of? also keep in mind the truck will start and run with fuel down the intake.

oh yeah and i tried to pull codes and it came up clean, no check engine light either.

thanks for any help

-Jalil

bigtruck21 · July 29, 2003

I don't know...are the injectors bad or do you have a blockage somewhere?

americanmuscleman · July 29, 2003

If you KNOW you have 40psi of pressure at the fuel rail, and you KNOW you have spark at the plugs... it can only be an electrical problem at the injectors. The injectors are fired through electric pulses, and if your wiring harness has become frayed or burned, maybe thats not getting the signal to the injectors to fire. It could also be your computer. Sometimes for no reason some of these GM computers just give up the ghost. I would be willing to bet though its a problem with the wiring going to the fuel injectors. Maybe a ground strap came loose or something.

Another idea came to mind. Make sure the computer is grounded like it should be. If that strap came loose, that can cause problems. There is also likely a grounding wire that attaches to the passenger's side of the block just under the driver's side cylinder head. You might see that's come loose.

ISRACING · August 6, 2003

I knew that it wasn't anything computer related, and after troubleshooting, and using logic, I determined it to be the fuel pump based on the symptoms. I pulled the tank, however did not replace the pump I pushed the pump and steel line tight into the rubber coupler then submerged the unit in a bucket of fuel, and the fuel PSI went to 60 with the pump on and held up without bleeding back to zero. The truck then started and ran just fine. I tweaked it so it couldnt' come loose again and reinstalled the whole unit and it now works great.

SO if anybody has the symptom where the PSI isn't enough then bleeds back to zero, it's either come loose, or the check valve is bad and the pump needs to be replaced.

thanks guys.

speedshifter · September 7, 2003

Glad you fixed it! Never heard of that happening before. I know a common problem with the Vortecs is the poppets sticking on the fuel injector lines. GM has just released new replacement direct injectors instead of the injector/poppet system. This system not only is flawless, but performance is supposed to be better as well.