Two years ago I went to the track and ran 15.6, last year I couldn't get under 16.1 with the same mods. In between I had been having problems with the car accepting a tune. Then about 5 months ago I stopped at home, went out to start the car and it wouldn't start. I ended up needing to replace the PCM, which was thankfully under warranty. So now I have a car that runs, but its still not back to normal. When I first brought the car into the mechanic they thought I might have jumped timing, but found a bad PCM after further testing.

I was told that the Eco can jump timing and not lose compression but don't know if that would cause the car to accelerate slower or not. Also, if the timing belt tensioner managed to break would the car run at all? Any ideas would help.

If your jumped timing say one tooth, you would have a miss at low RPMs, but would smooth out as RPMs went up,


- 2004 Cavalier - 124k, owned since new

Truly the chances that it jumped timing that long ago and still has not had more problems is unlikely. If it jumped timing something allowed it to (like bad tensioner), which would allow it to keep doing it until it smashed the vavles into the pistons. When is the last time it had a basic tune up? Has a compression check and leak down test been done? YOu mentioned accepting tunes, so has the ECU been reprogramed by someone? For what exactly?



FU Tuning

Basic tune up? I've changed the oil (duh) and replaced the filter on the CAI.

How would I do a compression and leak down test?

All I was doing with the tuning was adjusting the spark map with Evilmonkitar's assistance. I DID save the stock tune, so that's what is back on it until I can figure out whats going on. No tuning was done with the 15.6 pass.