Solved the Misfire

The stock coil that was in my 1986 Saab 900s

How's this for an interesting symptom?



I discovered/noticed that the car never misfired when it was snowing. Odd, so I went through the possibilities:

1. Temperature
   I've had the car misfire in temperatures as cold or colder than the temp when it's snowing. So that's probably not it.
2. Moisture
   That could be. But how to confirm that?
3. Headlights
   I always have the headlights on when it's snowing.
4. Driving more slowly
   I've had the misfire happen when driving slowly as well, such as in traffic or on winding side roads. So this is doubtful.

I could easily check the headlights thing. So while driving and getting the misfires, I switched the headlights on. The misfire was gone! What could POSSIBLY do that??!?!?!?!?

I thought perhaps the alternator, or more precisely, the voltage regulator had failed. So as soon as I got home I pulled out the multimeter and checked. 14.10v rock solid, only varying by .04 when revving the engine. So that's not it... But when I turned the headlights on, the voltage dropped to 13.90. Hmm...

So what could possibly be impacted by a .20v change?

I had one big possibility, and one small one. The big one is the hall sensor in the distributor. The plastic clip that holds it in place was broken when I got the car. If it wiggles out of the hole enough, it can short against the metal body of the distributor. I had it wired and siliconed in place to prevent any more shorts. But could it have been weakened?

The small possibility was the coil. I've had bad coils before, but they came from the manufacturer bad. I've never seen one fail in use other than leaking its oil out or bursting. Neither of which had happened to mine.

I ordered a distributor from a used parts dealer, with the hall sensor installed. In the meantime, I went junkyard hopping for a coil. I found a shiny one in a 1986 900 turbo with the 8v engine. Being mistrustful of shiny stuff on a car, I also grabbed the coil from a 1988 9000 with the 16v engine. $20 total for the two from UPullNSave.

When I got home I put the shiny coil in the car and went for a test drive. That solved it! My old coil was so tired that the tiny voltage difference was enough to cause it to fail when warm. GAH!

"New" shiny coil from a 1986 900 turbo 8v. Still a Bosch...

Today I was installing the replacement distributor (I've got it, might as well use it) and noticed the coil from the 9000 was swollen. Off to the trash it goes!

BTW: Has anybody ever actually gotten that @#$%^ cap back on the coil properly? Frustrating...