Starting Problem (Injector Pulse)

[Bryan C. King]

Got a 99 1/2 ton 4X4 pickup with a 5.3l in the garage. 150K miles. Having some problems that I hope someone has run into before.

From what I was told the owner of the truck shut it off one day and could not re-start it. Brought it to a local garage and they attempted to hook up a scanner to it. The scanner would not communicate with the ECU. They found a fuse (unknown which one because they don't remember) that was bad. Replaced the fuse and could communicate and had no codes. They hooked up a fuel pressure tester to it and they replaced the fuel pressure regulator. That did not help and now I have the truck.

This is what I have done and checked. Truck has spark, cranks over and fires for 2 seconds and suddenly dies out. I checked fuel pressure and at prime it has 60-65 Psi. For the whole 2 seconds that the truck does run it seems to hold 55 Psi fuel pressure. I took my noid lights and checked the injector pulse. I have pulse when cranking the truck over but it suddenly dies out when the truck fires. So I am only getting injector pulse while cranking but not at the run position.

I have asked several people their input. One theroy was that the factory security system was not allowing the truck to start, but if that was the case then why fire and run for 2 seconds and die right out? Another was bad ECU, but again why would I get injector pulse at crank but not in the run position when the truck fired up? Another theory was crank sensor, but if that was bad I would have no ignition spark.

Hoping that someone has some good helpful imput, any helpfull suggestions or comments would be greatly appreciated. Thanks in advance

[GMMerlin]

Originally Posted by Bryan C. King

Got a 99 1/2 ton 4X4 pickup with a 5.3l in the garage. 150K miles. Having some problems that I hope someone has run into before.

From what I was told the owner of the truck shut it off one day and could not re-start it. Brought it to a local garage and they attempted to hook up a scanner to it. The scanner would not communicate with the ECU. They found a fuse (unknown which one because they don't remember) that was bad. Replaced the fuse and could communicate and had no codes. They hooked up a fuel pressure tester to it and they replaced the fuel pressure regulator. That did not help and now I have the truck.

This is what I have done and checked. Truck has spark, cranks over and fires for 2 seconds and suddenly dies out. I checked fuel pressure and at prime it has 60-65 Psi. For the whole 2 seconds that the truck does run it seems to hold 55 Psi fuel pressure. I took my noid lights and checked the injector pulse. I have pulse when cranking the truck over but it suddenly dies out when the truck fires. So I am only getting injector pulse while cranking but not at the run position.

I have asked several people their input. One theroy was that the factory security system was not allowing the truck to start, but if that was the case then why fire and run for 2 seconds and die right out? Another was bad ECU, but again why would I get injector pulse at crank but not in the run position when the truck fired up? Another theory was crank sensor, but if that was bad I would have no ignition spark.

Hoping that someone has some good helpful imput, any helpfull suggestions or comments would be greatly appreciated. Thanks in advance

It sounds like a theft deterent concern.
If there is a TD problem the engine will start and run for 2 seconds and shut off.
Is the Security light on or flashing?

[dexter452]

it sounds like the passlock is acting up , to relearn the passlock, turn the ignition key on ,turn all of the accessories off and close the door wait about 20 minutes, and it should be relearned. turn the key off , wait about 1 minute. turn key on listen for fuel pump,crank and it should fire up . if it does not and you are getting no codes and i will guess that the fuse that blew is the one marked ecmb , main power , it is probably a bad ecm.good thing is that they are cheap exchanged thru gm.if you have anymore question please ask

[Bryan C. King]

Exactly what the problem was, Passlock is being fixed now thanks for the help......

[dexter452]

it sounds like the passlock is acting up , to relearn the passlock, turn the ignition key on ,turn all of the accessories off and close the door wait about 20 minutes, and it should be relearned. turn the key off , wait about 1 minute. turn key on listen for fuel pump,crank and it should fire up . if it does not and you are getting no codes and i will guess that the fuse that blew is the one marked ecmb , main power , it is probably a bad ecm.good thing is that they are cheap exchanged thru gm.if you have anymore question please ask

[dexter452]

sorry for the double post not quite sure what happened there. pass lock is a resistor based system and as with any resistor there is a tollerance percentage ,but the reader only has about a 1.5% tollerance and after time the hall effect ring resistance changes,so the new resistance must be learned.great system but does at times do weird things.