ever since i've had this car, i've had issues with the way it ran, mostly bucking/hesitating, but i just now got a hold of autotap. I got the car in June, non running, and put an new GM opti in it to get it running, the car was negelcted and I assumed it just needed some freshening, but I never got it running right with new opti, NGK TR55s, wires, new MSD coil, front o2s, checking for exhaust/vacuum leaks. Anyway, running the total current misfire data, I get a pretty steady count, usually around 150 total per 200 rpms (I know, a lot). It is somewhat affected by RPMs/throttle angle/load, but is always present. Cylinders 7, 4, and 5 show no 0 misfires, but all others do, with 8 and 3 being the worst and 2 being intermittent, but the total misfire graph is pretty flat across, with only a sudden change in the number of total counts (depending on how i'm driving, but haven't found a direct correlation), then steady again for a few seconds, but never anywhere close to zero. Maybe my Opti is 120 degrees out? I had problems getting it in, but a friend of mine got it to slide in pretty easy. I know it's slotted so it should only go one way, but i've heard of others getting it in wrong and looking like it's on correctly? Any help, ideas appreciated.

 

Why don't you try connecting an inductive timing light to each cylinder and see if you detect any plug misfirings.

 

The scantool is correct, it's misifring, just trying to figure out why with all the new parts, but I did check it today with the light to see just to be sure. results like the scan.

 

So are you saying that you can see the spark misfire by using the timing light?

 

yes, cylinder 8 doesn't fire very often (like my scan results) and the others (3 and 2) giving me erratic firing (same as scan results). And I know the car is missing, it runs like doo-doo.

 

You might want to check the power supply circuit for the injectors. One fuse/wire (circuit 639) supplies #2, #3, #5 and #8 with +12V power. I just saw a post yesterday where someone claimed they found the insulation rotted on the injector wires in the harness. Not sure if it relates to your problem, but is interesting that your misfires are only on 3 of the 4 cylinders on that circuit.

 

All injectors are firing, I had lifted the fuel rail off and cranked the car to check for a leaking injector a few weeks ago. there's fuel going to those cylinders, just no spark, the exhaust is so rich it'll make your eyes water.

 

First off, I don't know how long it's been run with no spark but you should check the oil for fuel contamination. Souping a cylinder will damage the rings as well as the cylinder wall. Don't run the car long like that.

As for your problem, it's doubtful the ICM or coil are the problem since it's consistantly the same cylinders. However, it takes very little time to check the coil with the same timing light you checked the cylinders with. You obviously want to be sure the coil is firing consistantly.

Your problem would then lie in the distribution of the spark. That is, after the coil. It would have to be in the wires, distributor or spark plugs.

One interesting thing you could do to pin point the problem would be to swap the wire and plug from a bad cylinder with a good cylinder.

It's all over but the crying now.

Dave