Just another reason why I am glad I do my own servicing. Gawd damn parts replacers as I call them...replace parts till the problem hopefully goes away. Diagnosing is beyond them, I guess.

My BMW motorcycle operates on the "wasted spark" principle because it only has one coil with two leads going off it. That had me thinking to have you check if your wires were connected in the right position. There are firing times where it won't be as noticeable.

 

Not sure how this happened but my 993C4S had it's lower exhaust wiper Dist plugs wires going to the intake plugs ! Just to make sure: Dist 1 is the lower Dist and Dist II is the upper Dist that is near the fan. Then why do they called the Primary Dist (the top one) the Primary Dist II ? Wouldn't one think the Primary Dist should be referred to as I ?

Thanks

 

Yes. Distributor I is the lower distributor and II is the upper distributor closer to the fan. Wires from distributor I (lower, belt driven) go to the upper plugs. Wires from distributor II (upper, shaft driven) go to the lower plugs.

Distributor II is called primary because it is shaft driven. Distributor I is secondary because it is belt driven.

 

I thought this was strange too, why label the belt driven dizzy as I and the shaft driven as II?

But then why did they not seal the dizzys so we can leave our cars outside in heavy rain all night when we are on holidays and have to spend who knows how long trying to start a car with a wet ignition... oops I'm feeling a rant moment beginning... Sorry.

I also discovered my car has hotter plugs meant for a 993TT, they've been there since I bought the car 10 years ago now. Looks like I'll be getting my hands dirty soon.

Well done on solving the problem and thanks for sharing.

 

Good eye!

But why are there crinkle cut french fries in your engine

 

It makes no logical sense to have the lower belt driven the Dist (I) the Intake source of plug-firing. I would think the Primary (II) Dist should be the Intake source of plug firing.

 

Since Germans read left to right, the left one got labeled I and the right one got labeled II. That's my guess. Just a label as you say. Wow. 10 years!

Thanks. Its nice to actually diagnose something instead of throwing parts at it. The 'fries' are from the cedar trees at my parents house. I made a poor parking choice one day. I think a few fries are still in there.

I would like to think that this was thought through by the designers and they felt it was better for Dist II to fire the lower plugs if the distributor belt broke. Not sure myself which would be better, or why one would be better over the other.

 

Thanks for clearing up the German way of seeing things. They have been wrong in the past of course. I always thought the secondary dist fired the wiper exhaust plugs to clean the burn and thus allow higher compression and lower threshold of pinging. And I always thought the Primary Dist II would be firing the Intake plugs as those plugs are critical to the operation.

 

AH! You really were typing 'wiper'. I thought that was just a typo or cut/pasto. As in mop or cleanup. I see now.

My understanding (belief?) is that both plugs fire at the same time, as I don't see anything in the layout/design of the electronics that tells me that the DME can fire the two plugs for the same cylinder at different times. Would like to know if you have any specific information that can confirm or dispute this.

 

"My understanding (belief?) is that both plugs fire at the same time, as I don't see anything in the layout/design of the electronics that tells me that the DME can fire the two plugs for the same cylinder at different times. Would like to know if you have any specific information that can confirm or dispute this."

If they fired at the same time then it would not matter which cap wires went to Intake or Exhaust; in theory then you could swap the two dists and nothing would change as "both plugs fire at the same time."

 

"in theory then you could swap the two dists and nothing would change as "both plugs fire at the same time.""

And in reality, both plugs fire at the same time. The dual plug system was
used to reduce the likelihood of detonation allowing higher CRs and timing
advances. Mercedes Benz used a system similar in the late '90s and early
2000s on the 6/8 cylinder engines.