96 c1500 4.3 vortec rotates but does not start

Recieved a call from friend about 10 days ago telling me that his truck would not start. Apparantly he went into a store, came out fired up his truck, drove across the lot to a gas station, put in the gas and the truck would not start. Engine will rotate, has spark, and newer air filter. He told me it was like someone had shut off his fuel. A check of the fuel pump showed that the relay was working but the pump was not coming on. I told him we needed to check the wiring, but against my advice he changed out the fuel pump. The truck fired right up and he drove it home. Great, problem fixed! Nope. 2 days later I get another call saying that the truck was shutting off on him while he was going down the road. I told him he had a wiring issue and needed to rewire the pump. Somehow when he was running a hot jumper wire he blew one of the ignition fuses, so the truck would not start again. Not realizing the fuse was blown he removed the jumper wire and started searching for what was wrong. Found the fuse, replace it, the pump operated properly and he drove the truck for another day. Again I get a call, the shutting down continues with no Check Engine light. Only it is getting progressivley worse. I told him to call the dealer, and recheck everything he had done. changed the fuel filter and now the truck will not run at all, Unless you dump gas in the intake, even then it will only run for a few seconds. They said to check the fuel injectors with a noid light. he did that and also checked his fuel pressure (about 65psi). He pulled off the upper intake and cleaned all the gunk out of it and the injector tips, and put it all back together. still nothing. The truck still has spark and turns over great. I went to check it and we installed a new battery and checked the camshaft and crankshaft sensors. From what I understand they both had 12 KOEO power and in the area of 4.5v on the signal wire. We removed the distributor cap and cleaned all the contacts inside. Also cleaned the button. While removing the button I noticed there is significant lash in the distributor shaft movement back and forth. (Maybe the problem). Put it all back together and still nothing. Checked the electronics with a scanner and found that engine rpms are moving when cranking the engine. The injector pulswidth will jump up if you dump gas into the intake and the engine fires up for a few seconds. No pulsewidth if the enigne does not start. The coolant temp showed about 34deg C with and ambient temp of about 80F. We installed a jukyard PCM to see if that may be the cause, still have the same problems. Reinstalled the original computer and still will not fire up. All fuses and relays check ok. I am out of ideas. Please help this is driving both of us nuts. Sorry if its not clear, there has been alot going on.

check throttle posi sensor which determines fuel delivery based on throttle valve angle.gry wire is 5v ref voltage,drk blue tp signal to ecm,blk is ground. idle throttle voltage on drk blue is apx .5v and full open 4.5 volts. That 65 lbs fuel press was at rail correct?good luck

Sorry forgot to include that. I did not actually check the voltage on the TPS, but I did verify that its value in relation to the pedal is correct. tps moves between 0 and 100 smoothly when pressing pedal. And yes the fuel pressure was checked at the rail.

check for voltage, resistance is not what the computer reads in this case.and tps is what determines amt of fuel injectors release. since you have fuel at rail and spark is ok since if you introduce fuel into intake it runs, seems injectors not giving cylinders fuel.Oh and make sure ground is good on tps cause without that the voltage (if there) to ecm will not change with throttle position.Also maf sensor can cause same prob since it checks air flow and also allows ecm to calculate fuel delevery make sure air box etc is clamped good to throttle body (NO AIR LEAKS). I dont see on your list.It also has batt voltage on C term fed I believe by pink wire, ecm 1 fuse I think is 20 A.













i

ok, just an update for future research, Turned out to be the fuel pump. I finally told the guy to go pay the dealer the diagnostic fee and be done with it. Took them 5 miniutes and they said that the new fuel pump was defective. It sux, but the truck is running now. However he now has a new problem. Now #6 cylinder is over fueling. I figure an injector may be stuck open, Guess the fun aint over yet. Thanks for your input ronaldk.

hay thanks for posting back looks like the 65LBS pressure he read was a little off. And your probably correct about that injector. Glad for you and your friend ,hard when were not there. Again thanks for posting back