Need a pro to Diagnose

[Ryan Moilanen]

Yeah I will definitely not be going back to that shop waste of 100$ diog fee..if I add starting fluid it will shoot out my manifold with fire..

I can also hear it backfire out the tailpipe

 

[Scout1069]

These trucks have a common problem with the ignition modules on the distributor. I had the same problem with my 1988 C1500. I replaced the whole distributor with a Duralast from Autozone and issue was resolved. Backfiring is from an ignition timing problem. In the old HEIs it was usually because the distributor was put in 180* out.

 

[El Tigre]

After verifying fuel pressure,I examine wire harness/grounds for wear/damage...

 

[7thdarkangel]

These trucks have a common problem with the ignition modules on the distributor. I had the same problem with my 1988 C1500. I replaced the whole distributor with a Duralast from Autozone and issue was resolved. Backfiring is from an ignition timing problem. In the old HEIs it was usually because the distributor was put in 180* out.

Had the same problem in mine a while back. 2 modules later (3-4 months apart) I ended up putting a new distributor in and didn't loss another module for the life of that motor.

 

[blackburb]

Yeah I will definitely not be going back to that shop waste of 100$ diog fee..if I add starting fluid it will shoot out my manifold with fire..

Sounds like bad timing caused by a worn or improperly positioned distributor... could also be caused by worn timing chain. I would check the distributor first. My 1997 vortec backfired and failed to start, as you describe, when my distributor(actually a cam position sensor since the cpu controls timing) was installed incorrectly after swapping my motor with a new GM crate engine. I also discovered the old distributor with 218k miles was so worn it could not hold timing. Using a scan tool the shop I took it to showed me the CMP/Retard was floating between +-5*. The computer needs to see no more than +-2* Any more than +-2* and the CIL will come on and throw a P1345 code. Was your CIL illuminated prior to the truck shutting down?

The distributor gear usually wears out first. You can identify a worn distributor gear by checking for sharp/razor edge teeth. I have also noticed the distributor body will crack where the cap is screwed down making the cap slightly loose.

Replacing Vortec Distributor:
Vortec distributors require a very specific install procedure that even dealer tech’s have trouble with. Here’s a good video on how to remove/install a vortec distributor.

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You will need to do a CMP/Retard aka: cam/crank correlation after the distributor is installed. I use the DashCmd app on my iPhone to do this. Otherwise you will need to take it to the dealer or a shop that has the GM Scan software and knows how to use it.

FWIW: Oreilly’s has rebuilt distributors with lifetime warranty... however, you get what you pay for. I’ve replaced the Oreilly’s distributor twice in 50k miles, once for worn out distributor gear and second time for rust under the rotor. Oreilly’s no longer carries the same rebuild brand that I have so it is a PITA to warranty, it usually takes 6 weeks every time I have to replace the distributor.

One more item to check is the wiring harness for the Crank position sensor. I had multiple undiagnosed engine shutdowns with no codes, good fuel pressure, good spark, good compression. The GM tech found a wire coming from the Crank position sensor grounded to the block. He repaired the harness and all good for the last 200k Miles.

 

[El Tigre]

I cut "windows" in the top of an old cap to allow me to see inside while motor runs. Shim throttle to slightly over 1000rpm. Slowly rotate distributor housing back,and forth. Watch spark lean one way,then the other. Set at spark straight,and short. Tighten clamp,and replace with normal cap. Should be close enough to not trigger light,if not dead on.

 

[Chevyguy78]

My guess is your distributor. Mine did the same thing. It took me weeks to diagnose it. Mine had the same symptoms as your describing.

 

[wheelman]

Look.bring up number one piston on the compression strook.raise up your distributor cap.rotor should be pointing to number one plug wire.on cap.

I have seen it where the plug wires on the cap.is one place off all the way around the cap.making the engine out of time.

Next with cap back on.spin the engine and with number one plug grounded to exhaust. Manifold.see if you have spark.no spark.ignition module most likely bad.in the distrbudist.or where ever it is mounted.

On my 1996 Chevy van.i found on my 350 vortec.i had to use the dealer cap.after market cap was no good.if you are going to pull the distributor

Check JEGS they have some deals.i like rockauto too.