Module madness...part 2

[dyeager535]

Not to discount your thought, but I would think that perhaps you'd not see *a* variation in timing with a stretched chain. The way I'm looking at it, with no load you might be able to turn the crank CW/CCW and see some "slop" at the rotor, but with the engine running one direction, any slop might be taken up and thus keep steady timing, just retarded a bunch?

If you go way beyond 0* base, then reconnect the bypass, does it change anything? Most only see about 4* advance before they start running into detonation problems, if the chain is causing any issues, I would think you'd get a bunch more advance (or retard) before having issues. Based on rotor/cap "phasing" shown in your picture, the chain would either have to be way off in retard, or a bit off in advance.

You're confident the timing gear isn't a tooth or more off, leaving the cam physically advanced or retarded?

 

[Irish1941]

My experience with a bad timing chain is the timing won't be solid. It'll move around under the light. Stretched or jumped a tooth, it can't be timed right. If it was more than one tooth, valves would slapping top of the pistons.
Timing is perfect on this one. It advances correctly.
It'll also rattle against the cover which can/will set off the knock sensor. Plugs will be fouled due to late timing. Plus you'd hear the valves being out of time thru exhaust and the engine would be shaking constantly as entire valve train would out of sync.

The truck is in time but is just having spark issues. The vacuum gauge reads perfect with zero movement at 21"hg (130' above sea level) as well so there is no mechanical problem inside. No vac leaks, valve problems, flat cam lobes, or no timing stretch.
My vac gauge is my first go-to tool anytime there is a problem and can usually point me in right direction pretty quick. This is why I think it's an electrical/ignition issue. I'm having a few extra ICMs tested today just to rule that out completely.

I'm still leaning towards it being cross fire and rotor phase in ignition system. I'm not completely knowledgable about the '89-'92 ESC module other than knocking will make ECM to advance/retard timing or when ECM loses contact with distributor, both throwing code 42. Could it be possible ESC is part of problem with no codes?
There are no stored codes nor does SES light come on.
*
Thanks for all the input. Much appreciated but trans went out yesterday so now this has to wait. Never ends...

 

[dyeager535]

Yep, can't win. Been trying to tune my truck for years, haven't been able to get rid of a tip in stumble and seemingly random "heat soak" related idle issue. Threw a pressure tester on it after seeing fuel rail surface temp of 145* (intake was 160*), 25PSI. Get to drop the tank or replace the regulator, more testing tonight to find out which.

As far as I'm concerned, at least with the GM OBD1 junk, they are too primitive to have covered a bunch of the potential failures that should trigger a CEL, but don't. I know more than a few people who say they can run without an O2 sensor and get no CEL.

Do you have a GM service manual that you can reference for the troubleshooting charts? *Normally* they will cover things like ESC that can't really be tested, simply by process of elimination. MOST of the ignition stuff is pretty easily tested, the ESC to my knowledge is not. As long as there is no CEL for ESC, and the system retards when knock is detected, that's about all I know to verify it's working properly.

 

[Irish1941]

I have the trouble shooting flow charts but never dug that deep for ESC but believe you are correct about ESC. Either is working or it's not.