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Rough idle when secondary distributor disconnected - SOLVED

 
Old 10-06-2012, 06:34 PM
  #16  
IXLR8
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Originally Posted by BesideTheBox View Post
There is a service note at 61K miles in November, 2009 that mentions a "slight stumble at idle". They performed a 60K service that included replacing the spark plugs. Funny that a 60K service was performed again at 68K miles in September, 2011 that also included replacing the spark plugs.
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.
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Old 12-01-2013, 01:16 AM
  #17  
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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
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Old 12-01-2013, 03:01 AM
  #18  
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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.

Originally Posted by C4S993 View Post
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
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Old 12-01-2013, 07:24 AM
  #19  
Aussie Alan 993
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Originally Posted by BesideTheBox View Post
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.
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Old 12-01-2013, 09:11 AM
  #20  
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Originally Posted by BesideTheBox View Post
Thank you all for your tips and hints.

The next time I have the car jacked up and the engine tray removed I will get everything returned to specification.

Interesting how the dual plug design masked the issue except for an occasional miss.
Good eye!

But why are there crinkle cut french fries in your engine
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Old 12-01-2013, 09:26 AM
  #21  
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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.

Last edited by C4S993; 12-01-2013 at 09:52 AM.
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Old 12-01-2013, 11:58 AM
  #22  
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Originally Posted by Aussie Alan 993 View Post
I thought this was strange too, why label the belt driven dizzy as I and the shaft driven as II?

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.
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!

Originally Posted by killsbugsfast View Post
Good eye!

But why are there crinkle cut french fries in your engine
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.

Originally Posted by C4S993 View Post
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.
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.
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Old 12-01-2013, 12:18 PM
  #23  
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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.
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Old 12-01-2013, 12:41 PM
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Originally Posted by C4S993 View Post
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.
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Old 12-04-2013, 02:39 PM
  #25  
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"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."
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Old 12-13-2013, 12:34 PM
  #26  
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"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.
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