rebuild engine in my truck 90 chevy 4x4 4.3 m5 tbi it won't run where it's supose to be timed, 0*, it runs pretty good at 10* to 12*, but will still die out. it seems to be worse cold. i've had my scanner on it and no codes or anything that jumps out at me. i set the valves cold when i built it and set them hot after it fired up. setting here thinking i wish i'd checked the vacumn on it. i replaced the cap and rotor plus the wires and plugs while i had it apart. any ideas? thanks

 

Welll...
I normally start in the dark and look for an arc...
and then start pulling plugs...

Im not sure if you said you checked for a vacuum leak
or wished you had...

 

any more ideas?

 

You have the distributor off a few teeth! Pull the distributor out and move it clockwise a few centimeters. I'm sure you know how to realign the oil pump drive when it off a little.

 

i donno if that would make a difference. Even if its inserted off a few teeth, one just turns it to correct the timing after startup. No matter how its inserted (reasonably close to tdc), the you can always get the propper time just by turning it to compensate for the error. I personally think ist a problem w/ the igniton system, sounds like a weak ign coil or possibly a vacuum leak.

 

Yeah I don't think the few teeth will make such a difference because of the later adjustment that can be made. I'm tending to lean to a potential vaccum leak.
Right now I'm driving the same truck as you (I'm taking my heads off of the IROC) cept it's a 3L80 and it seems to like 6* advance the best. Idles well with 6*. It was idling rough awhile back and turned out to be a bad EGR valve. I didn't think an EGR valve could make it idle rough.

 

bad egr will do it... had the same problem when my computer in my s-10 tahoe kept opening the valve at idle. Quick reset solved all that.

 

except for the burnt piston and valve it ran good and idled good before i did the rebuild so i suspect it is soemthing i did. it did set for 6 months after i rebuilt it before i got around to starting it, since i was working away from home. i doubt the distributor is off since i can set te timing anywhere i want in the correct range. i've not had a chance to do anything more to it since i posted this. i'll put vacumn gauge on it today and check the egr. thanks for all the ideas

 

This may be redundent but double check the firing order and maybe reset the IAC....

 

Sounds kind of like a vacuum leak....

 

thanks rb, that's what i was thinking when i was sitting here typing the original post, that i should of checked vacumn because it sure sounds like a leak. i put a gauge on it and it is, oiled the side of the intake real good and fixed it. time to r&r the intake and swap gaskets, damn it.