1995 Chevy S-10 Blazer - 4.3 L Vortec V6 (vin W with PCM) - This is the distributor style with vertical cap posts. 230,000 miles original owner.
EDIT: Please click on link below to see a photo of distributor. It is the "DI" style, not "HEI", "HE" or "HVS". There are no mechanical counter-weights inside this unit. AFAIK, all timing is advanced by computer control.
Without going into the detailed recent history, I believe I've checked, replaced, and eliminated every other source or possible cause of my rough idle condition. I narrowed it down to the distributor based on a lot of up/down play in the original, and I assumed gear wear, which gave me what seemed like a huge amount of rotational play (~ 3 to 6 degrees).
So I replaced my original distributor with a Cardone Select part #84-1635. Not a rebuild, but supposedly "brand new". The truck definitely runs a lot better, but still not as smooth as I expected considering how many things were checked and fixed. (Yes, it's been timed to the factory spec of 0 TDC at idle (~650 RPM) with the computer timing wire unplugged.)
Since the computer timing wire was disconnected, I did not expect to see any advance on acceleration from idle, yet my timing light shows a timing advance. How can the timing advance by itself when the computer timing wire is unplugged?
With the computer timing wire plugged in, the timing mark seems to jump around. Is this normal? I was expecting the computer to advance/retard timing smoothly with engine acceleration, not jump back & forth.
- Do these two observations indicate excessive distributor slop?
Up/down shaft play on the original distributor is measured at 0.032" and not a huge amount of gear wear. For the number of miles and reading about how these gears wear out, I was expecting a lot worse.
Up/down shaft play on the new distributor is 0.021" <- this still seems like a lot to me, but I'm not sure
Since there was not nearly as much gear wear as I was expecting to see, I'm doubting and second-guessing this new distributor or that I've done everything possible short of an engine rebuild.
- What is the amount of up/down shaft play supposed to be? Is there an acceptable range?
Also, there is a tremendous amount of slop in the engine block hole where the distributor is inserted. The hold-down clamp is firmly holding the distributor in place, but when this clamp is loosened, the entire distributor moves side to side. Don't get me wrong, there is zero side-to-side in the shaft itself. I'm just talking about the entire distributor assembly moving side to side and back & forth in the hole after the gear is meshed and fully seated. Is this normal? I was expecting the ring under the collar to fit snugly in the hole on the top of the engine block. I should have tried fitting the original one back in just to answer my own question; and now I regret that I did not.
With the clamp loosened and the collar seated down firmly on its gasket, mine is very sloppy all around (+/- 1/8"). In other words, the hole is way oversized... is it supposed to be like this or is there something wrong with this new distributor? I assumed the distributor assembly supposed to fit snugly into the top engine block hole.
Edit: This third question was resolved by simply inspecting the original gasket. There is a circular indentation in the original gasket that is offset about 1/16" from the center point. In other words, the original distributor was also not self-centering in the engine block hole.
While at Auto Zone today, I asked to see the Duralast distributor. It's new (not rebuilt) and I believe made by Spectra since it used the same photo and part number. I did a really quick check on the up/down play and it was more than 0.030". That's about the same as mine with 230,000 miles. Either it does not matter and they all have a lot of slop, or these imported replacements are not up to spec. This is what my question here is mostly about... the correct GM specifications.
Remaining roughness in the idle was finally tracked down to a loose heat shield that was intermittently shorting out the spark plug boot for cylinder #4.
It wasn't long after my last edit that the overall roughness came back with a vengeance. White exhaust smelled of gas and I was completely out of ideas...
See "Edit #3" on my other question for the root cause.