Intermittent miss at light load.

[534BC]

Yep, I can sure go along with that.

Older chevies always wore out the timing chains because of plastic gears.

50 k - 60 k would see them very well worn and stretched. Mine has 180 k and now has run perfect, but wouldn't surprise me if it did the same thing as yours. I'll look forward to your post, Thanks.

[1996LTOwner]

180k, huh? When I was in D.C., I looked at the odometer and saw 188,600 miles even and thought to myself that I was actually going to get 200k out of it. Guess I'll know tomorrow if I will. It made it to about 188.7k. You may want to stick close to home. I was very lucky. I live about 100 miles away from D.C. and it waited until I was within ten miles of home when it quit. Good luck.

[1996LTOwner]

Update: Timing hadn't jumped. Since I had it open, I replaced it anyway. Chain was sloppy but the sprockets looked pretty good. NOT plastic as my brother thought. After more troubleshooting, determined that the distributor cap was shorting the coil input to the #4 plug, causing it to fire constantly and weakening or robbing the spark from the other plugs. Once I thought it must be what was happening, I looked under the cap and noticed that the #4 pathway runs directly next to the center post. Put a new cap on and with the new chain and cap, it purrs like it hasn't in quite some time. Noticed also that on the new cap, the #4 pathway has been designed with a seperation from the center post, must have been an issue. I don't know what it's like on models of different years, but the '96 was a BI**H. The oil pan was designed as a structural piece of the transmission / motor assembly. This made it virtually impossible to loosen the bolts and drop it a little. I got it together and it's running great, but it leaks oil at the oil pan to timing cover gasket. I'm done, I'm going to have a shop replace the oil pan cover tomorrow. I don't feel like unbolting the drive shafts, dropping the front pumpkin and axle assembly, loosening the motor mounts and raising the engine just to remove the pan. Anyway, I believe the timing chain and sprockets took care of the intermittant miss and slightly rough idle so it wasn't a total waist of time.

[Chris Stewart]

Regarding ignition timing, the computer controls and advances the timing until the knock sensor(s) complain then it backs it off then starts advancing it again, trying to maintain the maximum timing for economy & power. That's why disengaging the EGR system hurts fuel milage...without the exhaust gasses to "cool" the combustion process, the knock sensors pick up more detonation and the ignition timing spends more time retarded.
As long as the initial timing is somewhere in the neighborhood of OK, the computer takes it from there and constantly adjusts.
Fuel trims/O2 sensors are even worse...lol

[1996LTOwner]

ECM will only adjust so much. I had the distributor out about a year ago. When I reinstalled it, the truck ran but seemed a little rough. Just to be sure I had it back where it was, I moved it one tooth counter clockwise and it wouldn't fire. I then moved it two teeth clockwise (one tooth more than the first time) and it backfired. They weren't kidding when they wrote these engines are sensitive to the timing. I put it back where I had it the first time. Replacing the chain and gears, after 188,696 miles made enough of a difference that I could feel it the first time I drove it. Even if it was to the shop to fix the oil leak I created.

[BlazerLT]

I bet you this is a bad TPS.

[1996LTOwner]

What's a bad TPS?

[BlazerLT]

throttle position sensor.

[534BC]

Problem finally fixed by retarding the distributor shaft one tooth. Vehicle runs as perfect as it ever did. No more intermittant miss at light load. Man am I slow. Pic shows one broken tab for the first "fix" the second tab was broken today to retard the housing as well as the shaft. There's really not a lot of swing on this housing because of the intake.