Problem with 96 C1500
 

Is there someone brilliant out there who can help me troubleshoot a problem I have with my V-6 pickup? What I initially thought was trannie trouble is shaping up to be something entirely otherwise. The truck stalled while I was doing about 50 mph, up a very small hill, with cruise control engaged. It jammed down into a lower gear, surged the rpms (tach went beserk, and was vascilating up to about 3200, down to 1000, and back up for about 20 seconds). I pulled off the road, put it in park, let it idle and could hear a very unfamiliar noise coming from under the bed: a rather dull "howling" noise that I can't find much to compare it with. I just assumed it was the trannie because I had slipped a low gear on a couple of previous occasions (maybe twice in 6 months, while taking off from a dead stop, up a hill). So I checked the trannie fluid; it was bubbly but not low or terribly hot. I killed the engine, restarted, and put it in gear. Got about a half mile, and the truck started jerking (like one does when running out of gas). It even stalled. I repeated this procedure, but after the 3 stalling, I could not get it to stay running after starting it. So I towed it home. Had a friend (airplane mechanic) take a rough guess at it. He suspected the throttle positioin sensor, and/or fuel filter. I replaced both of those, and still can't get it to start. We ruled out the fuel pump because I just put an NEW one in it in April. But I did replace the fuel pump relay under the hood. I am getting fuel into and through the fuel filter. And even getting it up to the inline pressure valve located just before the intake point where the lines go into the throttle body. Just not sure if it is pressurized enough (just the presence of fluid doesn't mean everything's working okay, right?). So my questions: Is there something obvious I'm missing, or should check? Should I suspect the injectors (how do I test for that)? Before going to the lengths of removing the bed and pulling the fuel pump again (assuming I bought a defunct one) and other than simply seeing that fuel IS getting into the lines, what other way(s) can I troubleshoot the fuel pump? I'm praying someone wise can bless me with some advise worth following. Thanks for reading. -- Blu'sdriver

pressure
 

you need to check the fuel pressure. just because it has pressure dose not mean that it has enough. I'm pretty sure it should run about 40 psi. one problem i ran into on a 96 was that the truck would run great for about 10 minutes and then stall. the fuel pump was pulling to many amps and it was overheating the fuel pump relay. after i replaced the pump truck ran fine. one more thing i would check is your catalytic convertor. i have replaced several on 96-98 gm vehicles lately.I have put on no less than 6 convertors in the last month. that would explain that rattling you here under your truck. if this don't help then look at the trans a little closer.

might also want to check the proper forum as well, you'll get more exposure there.

have you checked you cat converter to se if it's clogged up?

on the 96 4.3 it should average 55 psi, the window is 52-58 i believe. it needs min of 50 to start, the cat. could also be an issue, crawl under there and tap on it, if its loose and rattling a piece could have broken off and is blocking the exhaust flow causing major back pressure. also have you checked for spark?