FINALLY GOT IT!

CMP Retard: -18.9 degrees


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Base on what I read about retard should be no more than 2 away from zero, I'm guessing this is bad, lol.

EDIT:
Changed the screen shot when I realized it wasn't above 1000 RPM.


Some references I found
http://www.automotiveforums.com/t350633-timing_vortec_engines.html

 

Great! Is this with the BAFX or did you get your original one to work?

Yep very bad. Undoubtedly going to need a distributor gear to fix it right. Simply correcting the CMP Retard doesn't fix or stop the distributor gear wear. At $40 I would just get the entire distributor I linked to and put a Delco cap/rotor on it (what I did on mine) but you can put a gear on your original if you like for about the same money. You should also put a aftermarket Chevy V8 hold down clamp on it so distributor can be turned for fine adjustment, but you will need to source a different longer metric bolt and use a washer.

P.S. Don't lose your distributor rotor position when distributor is removed (mark it and don't roll the engine over). If balancer ring has slipped, not doing this could make it very difficult to position on correct tooth. Not sure how much the CMP Retard of 18.5 would affect this, but doubt if it would be enough to move the rotor position to where it was shown early on. All will become apparent when you get CMP retard set to zero. Then marks should nearly line up when rotor is pointing to #6. If not the balancer needs replaced.

 

Whats up - any progress?

 

Edit:
Oops. Didn't mean to tag you, George. I meant @LesMyer


@George Yes. I was waiting for an extra part. Decided to replace the oil pressure sensor while I have the distributor off. I've seen this part fail leaking oil on my Dad's S10 before.

I have a new distributor installed. The one you recommended. Truck started up just fine. Had a longer crank than usual, but ran smooth. No misfires at first, but once the RPM came down to idle speed #2 and #4 started misfiring the most. It's still a random misfire across all but #6.

Also CMP Retard is still off. Not as bad a before. Definitely an improvement, but there's still another compounding issue to find.

I guess the next step is to actually drive it and check fuel trim numbers. I suspect fuel injectors and/or LIM.

 

Need to get that CMP retard in spec before continuing, IMHO.

Les

 

I'm guessing LIM or fuel injector doesn't affect CMP retard.
What else would cause it to be out of spec? Timing chain? With this ignition system being compouter controled, how would I make fine adjustments? You mentioned a V8 distributor hold-down so I can rotate the distributor's position to fine-tune. I'll look into it, but is that absolutely necessary with a system intended to be self adjusting? What if it self adjusts out of my fine-tune rotation?

 

I read that the temperature sensor for mass air intake also affects CMP retard. Is there turth to this?

 

That one is a absolute negatory on affecting CMP retard.

But temp sensor does affect mass air flow calculation.

 

It's the only way to adjust CMP retard, which does not self-adjust. Only thing that changes a locked down distributor CMP Retard is distributor gear wear and timing chain wear/stretch.

 

Alrighty then. I'll look around for an adjustable hold-down bracket. I guess I'll start looking on Amazon or Ebay for an aftermarket solution.
In the meantime I'll also play around with scan data and see if there's any slop in the timing chain by studying ignition timing.
Curious to know why GM designed a system not to be easily adjustable when the obvious solution is to physically adjust the distributor.