Ignition Issues Fix on SC with 964 Motor

[Jim Smolka]

Thought it would be a good idea to post how a ruff running 964 motor was fixed.

Initial problem:

Driving down the hwy and the 964 SC (1982 SC with 3.6) started to run ruff. Made it to a gas station and added some gas. No improvement.

For a couple of seconds it would run perfect. Most of the time, the motor would sputter and stumble. The car got home on a trailer.

Tried a couple of parts like a crank sensor. No luck.

Found out the motor would run better (but not perfect) if only one coil. The motor would run better (but not perfect) if on the other coil. But the motor would run terrible on two coils.

Replaced spark plug wires , plugs, caps, and rotors. The motor ran a little better, but still bad.

Replaced both coils. Car ran great for 4 minutes; then it went back to running bad again.

Took the car to the shop.

One of the new coils was bad (arcing at the top).
They fixed some magnetic type stuff in the distributor.

Car runs great.

[Vandit]

So if the problem was present before you replaced both coils, then the arcing problem w/ the new coil wasn't the cause? Do you know how they identified this arching problem?

Also, any more details on the specifics of the distributor fix?


I ask all this because I'm in the middle of sorting out a similar stubborn intermittent misfire. It started occasionally last winter when the car was up to temp and driving normally (never while racing). I replaced the caps and rotors (all were shot) and the coils and the problem disappeared for a couple of months including racing and street driving only to come back w/ a vengeance. Now it's to the point i can't drive the car. I replaced the CHT sensor and cleaned the ISV, that didn't help. Next step is wires and I'm currently pulling apart the intake for a cleaning, gasket/coupling refresh, and just generally have a look around for possible causes.