I havea 95 trans am that has developed a high rpm miss. Starts around 5,000 rpm. plus or minus a couple of hundred rpm. The engine is a 383 stroker and has previously run up to 6500 without a problem. Once it developed the miss, I replace the plugs, wires, ignition module, coil, and also the optispark. I replaced the opti with msd unit, and it still was missing. In desparation, I pulled it apart to see if the screw that hold the rotor on had loosened up. But they were actually fine. What else is left? I also replaced the plugs again, and when pulling the old ones out I noticed that one plug had the outside of the porcelan blackened with some kind of carbony soot residue. You could wipe it off by hand. What in the world would this residue be from? Any do you have any other ideas?

 

maybe your looking in the wrong spot. maybe valvetrain. such as a weak or broken spring...

 

well I viaually inspected all valve springs and there is not any physical evidence of any broken springs. The valve springs that are in there only have about 1200 miles on them though, so I doubt that they would be worn out already.

 

Its possible the springs when new were borderline sufficent, now that they have some heat cycles on them they have lost some of their initial pressure. All springs will lose some pressure initially then level off, some will lose more than others.

May also have a fuel issue, faulty/dirty injector.

The soot was under the boot? Was it in a line like a carbon track?

 

Yeah, the black soot residue was under the spark plug boot. And it covered most of the porcelan on the plug. I was thinking that there might have been a crack in the procelan, and the arc may have been jumping down the outside. But who knows....

 

I too am having this same problem when i get on it and get to about 5000 rpm it starts breaking up i just replaced the opti spark and put all new wires and plugs. I unpluged the msd box and it still happens.

 

Well today i think i might have found the problem. I took some electronic contact cleaner to the ignition control modular plug. Just to make sure that it was getting a good contact. So i pluged it back in and it ran a little better but i then went up to the plug and pulled on the wires again and the motor died. It trys to start but i think i need to get a new plug i think mine has a short in it. Tomorrow ill go and see if napa has a new plug and try it out but im pretty sure thats what was causing it to break up. cause if you try to force the wire in more it starts but if you wiggle the wire the motor dies.

 

Good find, hope thats all it is.