You should also clean your grounds, especially the one that connects from the negative battery terminal to the bellhousing. Just follow the negative line from the battery and make sure that connection is clean wherever it connects.

Alternator is still suspect... is the cold air feed tube still connected to the back of the alternator?

I did clean the grounds as the first course of action. That was in my first post. I'll recheck the bell housing one. And yes, I agree the alternator is still suspect. And so are the fans. While it's running much better now, voltage still drops _a lot_ when the fan kicks on. It recovers immediately, but I don't think they should draw so much current even just to start up. Yes, the cold air tube for the alternator is in place and solid.
-Neil

My S2 was doing the exact same thing when the fans kicked on. I removed the alternator and found that the brushes were almost completely worn out and there was corrosion on the connectors to the voltage regulator. Cleaning all of those up and a new voltage regulator really helped and it doesn't dip as much anymore when the fans kick on.

Electrical gremlins are the worst.

I found this guide to be helpful for chasing them down.

https://www.maniacelectricmotors.com/chstsycivote.html

In my car (924 turbo, different animal) the alternator was showing 14V but wasn't keeping up when other accessories were turned on....so much so that the fuel pump wasn't getting enough power. I replaced the voltage regulator -- no improvement. Ended up replacing the alternator and the gremlins went away....with higher voltage readings across the board....load or no load.

More updates...
- I replaced the ignition control module - no change.
- I cleaned the last ground on top of the bell housing - no change.
- I replaced the spark plugs. Way smoother engine because the old ones were as bad as I suspected, but still getting the hesitation just as often.
- I found the ignition wires are pretty badly dry/cracked, and I've ordered new ones.

I haven't replaced the distributor/cap, alternator, or ignition coil yet.

Currently, The system is staying around 14.4V when running. When the high fan speed kicks on, that will drop to about 13.6V or so. If I turn on the AC, interior fan all the way, headlights, fog lights, defogger, etc I can get it down to low 13V. I can turn the voltage regulator on the alternator down to 12.6V and it will actually still run smoothly except when it hesitates. Since it's maintaining 13.6V (measured at the battery terminals and in the dash gauge) even when everything is on, I am not too suspicious of the alternator.

My current theory...
I think the cracks in the spark plug boots are allowing the back two spark plugs (worst) to arc to the engine outside the combustion chamber. I suspect that those arcs are drawing a lot more current than a typical spark would, so the ignition coil is too discharged to complete the next few sparks too. That would cause me to miss several. That would also explain why the problem is worsening so quickly to the point that the car has gone from mostly fine to difficult to drive in just a few weeks. And it would explain why it really needed to get hot in order to happen at all before.

Anyway, new wires are on order.
-Neil

New plug wires, distributor cap and rotor, report back. Cracked insulation on plug wires will definitely cause misfires... I would bet this is your issue and is completely unrelated to your fans or alternator.

It'll be new plug wires if they get here first with the old distributor/rotor. If I'm able to wrench again before that, it'll be new distributor/rotor with the old plug wires. I'm trying to be as piecemeal with my repairs as I can be to find _the_ culprit, though the extra 1-1.5V I got with cleaning off the battery terminals and connections probably was a major contributing factor. And I'd argue the same for the crusty old spark plugs too.
-Neil

The new distributor cap and rotor are on, but the misfire is still there. It wasn't as bad, but I think that was just a result of the reduced heat/humidity outside last night. The old ones were a bit grimy/corroded, but they definitely weren't the worst I've seen.

Anyway, just waiting on those new ignition wires now... I'm out of spare parts at home.
-N

Damn... I ordered the wrong ignition wires for an 8V 944 motor. Gonna be a few more days.

Side note, the car completely died on me in the pouring rain yesterday. Needed a tow home from literally a quarter mile away. It was being extra stubborn with the misfires, kept stalling, and then I just couldn't get it to go again even though I was still moving 40mph down the road. And hours later, it still wouldn't ignite.

I went out tonight, with the old wires still, and I was able to get it to start. I am not sure what the difference was. I did wiggle the very crumbly/delicate cam position sensor and I also wiggled the reference sensor on the back of the motor. That might explain this, but... I wiggled both of them while it was running, and it made no difference. If something on them was truly that flaky, I would have triggered it.

Another side note, I realized there was another ground behind the bell housing even bigger than the one I already cleaned. It still wasn't that bad, but I cleaned it too.
-N

I was reading your posts, and im new at this posting, but you guys have or hav had my dream cars, i was wondering if you put your old wires back on, after you got it back home like you said , and your still waiting on other parts ? My 2 cents, hav you tried to run car while its tottally dark, because if it was arching, you will see it, and sometimes when engine is running poorlly the exhaust manifolds will turn red, or glow indicating a ignition problem, some spit out the throatle body, some out the pipes, and my c2 was acting wierd, i bought it used, im the kind yhat would rather put parts in it, and know what iv put on, instead of taking the other owners say, which is taken in consideration. After exchange on my alternator the grimlins went away, this jumping it off every 3 weeks is nuts, i gave it a tuneup, verified with tester that its putting out 14.volts, even old oil gets washed out with fuel and make a engine act up..hope you keep up the posts and get it back on track...

Higher humidity or wet weather will increase the arching. This is why some days it acts up more than others.

I replaced the ignition wires. While it was out, I also cleaned the contacts on the ignition coil. It needed that. I was super careful not to get any dialectric grease on any contacts, because I suspect that is what happened the other day when it died completely.

No change. Still misfiring. It will misfire more/worse with lots of power draws, but it will do it with nothing extra turned on either and the voltage gauge never dropping below 14V. Even with everything on, it stays above 13v. It will also misfire more/worse under load, like going up a hill, but it is hard to tell if going downhill just hides it more.

Brainstorming again...
Could be ignition coil acting up. Could still be the alternator I guess, but that seems unlikely to me. Could be a sensor (cam position sensor, flywheel reference sensor, or MAF sensor). Could be a bad solder joint on the ECU. No idea at this point - going to have to think on this some more.

Replaced spark plugs and checked the gap before installing?

Yep - they were already gapped correctly. The _old_ ones were way larger gaps after so long. I really hoped that was going to make a bigger difference than it did.
-Neil

Are you sure it’s an ignition-related misfire, and not fuel-related?

Also, at least on my 944, I’ve found that the voltage gauge in the dash isn’t very accurate. A good DMM, or even a voltage gauge that plugs into the cigarette lighter seems to work a lot better…

No, I'm not sure, because I haven't found the culprit yet.

However, the misfire behavior is tied directly to electrical system usage/output. It will get worse when using more accessories. It will get worse when the dash gauge is bounces lower. The dash gauge has been verified several times by a really nice multi-meter measuring at the battery. The dipping during the misfires is also apparent on that multi-meter.

Currently, I know my cam position sensor connector is crumpled to dust around New England. There's sugru holding it together instead. While the car feels strong, I do know that it will retard timing a lot if that gets disconnected. I don't see how that could have led to the full failure in the rain, but I'm going to replace that because it needs replacing. I'll see what effect it has. I'm bummed that I have to re-install the timing belt to do that it appears. :-(

-N

I think I've got it! I replaced the cam position sensor last night. I knew the connector on it was crumbled away. I had molded the pins with sugru to hold the thing in place. It was another thing worth replacing even if it wasn't the culprit, but I had my doubts because the engine should run without it (albeit badly).

It turns out the wire shielding on the engine harness side was pulling apart just past the stain relief too. The copper for each of the three wires was exposed to the elements and heavily oxidized, but this wasn't visible until I removed it. This was probably why the rainy day completely killed it. A little water there would have shorted all three pins. I know the ECU retards timing if the sensor is disconnected, but I'll bet that all three pins being shorted together would be worse.

I just took a short drive with every accessory I could turn on running full blast. I ran in gears too high uphill to force the engine to be overloaded. I did everything I could to get a misfire, but I didn't feel a single stutter. It was a short drive, but at least 10 times as far as every other time I've reproduced the issue in the past tests.

I've driving hundreds of miles since the last post without a single misfire. I used to barely make it a mile before the car became undriveable. I was sure I had it.

And then, after about 45 minutes of driving today, it started again. I felt a couple tiny misfires on the highway, saw traffic building up, so I got off the highway. And I must have stalled another 20 times forcing me to the side of the road again. It always restarted, but often the slightest application of throttle would just cause the tach to drop nearly to 0 or just stall out. I made it home, but it was tough. I could usually get a few bursts of speed right after a restart that I could use for momentum enough to get a decent bit of progress.

I'm wondering if some my solders on the cam position sensor are failing, because that wire was definitely warm/soft after the drive. If the cam position sensor signal was the culprit, then I'm sure an issue there would present the same way, but I really took care to clean the wires and use good shrink-wrapped connections, etc. I don't really think it could fail the same way it did before.

Anyway, I did notice something odd. The light on my driver's door lock was on toward the end of the drive. I know my central locking is a bit weird because the center console button doesn't work reliably one way or the other. But I know the light was off when I first got in the car. Sometimes it takes a few tries turning the key in the door to get it to go off. Anyway, I just know it's not working great, but I wonder now if that's tied to the alarm box near the ECU. Could a failing alarm module cause this kind of behavior? I know that can cause no-start conditions, so it must be able to interfere with ignition, but I've never heard of it causing issues after a car is started.

All in all, damn't... I do have a new/used fuel rail with fuel pressure regulator that I am planning to swap on tonight.
-Neil

You could try rigging an ammeter on the coil, if the spark gets bad maybe coil current would show it.
Bypassing the alarm module sounds like a good test, however I recall reading that some of the instructions on how to do this are incorrect.

A long-overdue update... I wanted to replace the fuel rail because of the modified fuel pressure gauge bung that scared me, but the seals I ordered for the injectors didn't fit right, so I got a different package from another vendor. It took awhile to square things away there. Now I have a proper fuel rail, new injector seals, and I replaced the fuel injector filters on each one.

My theory for the hundred-plus miles of normal driving and then bed hesitation again was a failure in my repaired wiring to the cam position sensor, maybe related to heat exposure. I opened up my shrink tubing and strain relief, and nothing was broken. I rerouted the wire and rebuilt the strain relief better with more heat shielding. I have purchased a new connector pigtail for the engine harness side, but I haven't replaced it yet. That's next.

Anyway, I didn't make it even a mile from home before the hesitation started again. Same as before again.

Next steps...
- replace the ignition coil of I can find one. I've replaced everything else in the ignition system, so I just feel like I should replace this too. It may be the culprit.
- replace the connector on the engine harness to the cam position sensor. I want to make this prettier anyway, and this certainly could be the culprit. Redoing all the solder repairs with more space can't hurt certainly.
- buy a fuel pressure gauge setup for the fuel rail now that I have the proper bung. I don't expect to see an issue there, but anything I can learn can help.