I'm new here but not new to mechanical and diagnostic work.

I am working on a 2000 Zr2 5spd 4x4 with 241k miles.
It has a new MAP & TPS sensor, MAF has been cleaned. All new filters and fluids. New upper and lower intake manifold gaskets. New spider. New plugs, wires, distribution cap and rotor. Battery.
The CEL is not on.

I bought it as a project and it was running rough and seller told me the intake gasket was bad, milky oil pretty much confirmed that. I did everything above except the spider at once and no change. So I did the spider yesterday and it started and ran great, smooth idle and good power.
Today it was still running good until it had been idling for 15-20 minutes and moving around a little so I revved it up a couple times. Huge backfire out the exhaust and it wouldn't start back for an hour or more, even with a shot of starter fluid.
Once it started back it would idle perfect but I gave it some throttle and it started to rev then just died and no start again along with a puff of exhaust out the intake.
I ran out of time to see if it would start back but I expect it will after time. I'm not sure where to look first.
Fuel pressure is 59 to 62 with key on and cranking ,it will hold for quite a while without dropping more than 1 or 2 psi. Vacuum stays right at 18 and holds when not running .
What am I missing ?

Also there are a couple small exhaust leaks and after the backfire and it starting back I put my hand over the exhaust pipe to check for moisture and was able to hold my hand over the pipe easily.

 

Are you sure the distributer is clocked correctly? Being one tooth off can cause a world of problems. The only way to change the timing on these engines is by using a tuner or have the distributer installed incorrectly.

 

It was running perfect yesterday and right up to the backfire today. I did mark the distributor and it went back in the same place. I think if the timing was off it wouldn't have started out of nowhere like it did. It seems like now it doesn't want to start or run when warm.

 

Here is a complete diagnostic proceedure for finding out why your truck wont start. It sounds like you already know that you have good fuel pressure so you can ignore that section. What you don't yet know is if you have spark with proper timing and fuel injector pulses. Backfires are often ignition timing related hence AJBerts comment.

Start with:

Do you have any codes?
Do you have 1" of strong blue spark with a regular cadence at two or more spark plug wire ends?
Report back and we will go from there

Here is the test sequence:

https://blazerforum.com/forum/2nd-ge...rticle-103750/


George

 

I will check those things soon but here are a few I do know.
1, strong blue spark at the coil.
2, no dist cap, rotor or gear play.
3, there are no codes.
4, cat looks like it has been pretty hot at some point.
5, no raw gas smell anywhere.

The truck was running perfect, drove it around some and got to 3rd gear and pulled a small hill smooth as could be. Gave it 3 good revs to about 2k and as I let off the 3rd one backfire out the exhaust, sounded like a shotgun and died. After some cranking and letting it sit an hour or 2 it started like nothing ever happened and ran a while so I gave it a small rev and it just died again. Had to leave it alone that point for other work.

 

You had strong blue spark at the coil when it would crank but not start and run?

George

 

Strong blue spark while running. I'm sorry for not specifying that. I will Che it while cranking May tomorrow.

 

We need to catch what your missing (fuel, ignition, fuel injection, etc) when it cranks but won't start so we can pinpoint your problem and then find the cause.


George

 

It seems like the coil wire was my problem. I don't know if it's bad or was just loose. The way it was routed near the heater hoses when they got hot or when revving and the engine moves it was causing a bad connection to the coil. I found it by accident simply because I did not like how it looked, I unhooked the wire at the coil and ran it a different way and now the problem seems to be gone.
thanks for all the replies and tips! I appreciate all the help I have gotten from this forum, now and in the past. Lots of good knowledge here.

Robbie

 

Glad you got it fixed.


George