I have a 2000 s10 blazer with a 4.3 vortec. Right around three months ago it started missing at around 2000 rpm and at highway speeds anywhere from 60-70mph. In total I've put about $2000 into it and me and my mechanic have finally found the problem. The timing chain and gears were so worn that you could put a bar on the crank shaft and turn it a little over 90 degrees and then the distributer would start to move! It was bad. This was causing the distributer to try and fire the #4 and #5 cylinders together. One would overide the other causing the miss. It only happened right before it was about to shift gears and at highway speeds because that is when there was the least amount of tension on the timing chain. All together i replaced plugs, wires, distributor cap, rotor, entire distributor, FI Spider, timing chain and gears, and the timing housing. This has been a long and painful search but I've found my problem. Hope yall find yours!!!

 

That sounds just like what mine is doing. It has a miss just before downshifting when you're going up a hill. Mine also has a hesitation when you take off. My Blazer has almost 200,000 miles on the body and I'm not sure if its the original engine. But it makes sense. I'm going to look into this.

 

how did you check you timing chain? with a deep socket and breaker bar? were you able to do it with removing the fan and fan shourd only? i would like to check my timing chain too without taking everything apart.

 

Remove the distributor cap. Remove the front skid plate (4WD). Have a helper rock the engine back and forth with a breaker bar and socket. Watch the rotor and see how much play there is. There should be a minimal amount there. Thats what I'm going to do with mine to check it. I'm having the same issuses with mine.

 

Hey guys, just how many degrees of play should be between the crank and the distributor? Mine is not symptomatic yet, but there is definitely 3-5 degrees of play in it.
Thanks!

Regards,

Thomas