Al Cody

I am testing the ignition coil on my 83 911.
I can't find specs for the ohms. Mine shows infinite between the small terminals and 0.7 between the tower terminal and one small terminal.
I have a new coil from a 944 DME and it shows infinite between the small terminals and 6.43 between the tower terminal and the small terminal...big difference! If I am reading the scale correctly that would be 70 ohms and 643 ohms.
Is my black 911 coil hooped? and possibly the cause of the ignition module failure?
Second question can the DME coil be used with a Perma-Tune black box on my 911?
Thanks. Al

HarryD

Al,

Whenever you have a question on Porsche Electronics, chances are that "Early_S_man" at the Pelican Parts BBS (http://forums.pelicanparts.com) has already answered it. Do a search with him as the "User name" and the terms you need to find out about.

Using coil and ohms, you will find this post:

http://forums.pelicanparts.com/showt...ight=coil+ohms

This should have your answer.

What is the problem you are having?

Al Cody

My stock Bosch ignition module failed. It was replaced with a Perma_Tune unit. Perma TTune states that a defective coil can cause the Ignition module to fail so I am looking for specs to check that my coil is not defective. My many Porsche manuals do not state a spec for the ohms for the primary and secondary coil test. I have seen references to 500 to 650 ohms for other coils, but not specific to the SC that I have. I have a new coil from an 87 944S that has the DME ignition. It shows 645 on the secondary side while my SC coil shows 70 ohms. So, something doesn't make sense. Or my SC coil is hooped...which is what I am starting to suspect. The car, however seems to run just fine. I don't want a repeat of the ignition failure, obviously.
Thanks for the reply.
I did search Pelican before I posted here. And found the 500 to 650 ohm spec probably from S man.

HarryD

Hi Al,

It is prudent to replace the coil if you suspect it is bad. A search here and at Pelican turns up a number of opinions on both the Brazilian Bosch Silver coil (bad) and reasonable substitutes. From what I can see, a Bosch blue coil and a MSD Hi Vibration Coil seem to be leading contenders for replacing the OEM Black Bosch Coil.

Is you Permatune unit one of the newer ones (since the ownership change)? The previous owners appear to have tried to blame everything but their unit for any failure and since it is potted, you cannot open it up to inspect. If you still have your stock Bosch Unit, you might want to ge it rebuilt for the same cost as a new Permatune and keep it as a spare.

Al Cody

Thanks, yea that's about what I was thinking.
It is a new improved Perma Tune which seems to have a better reputation than especially the silver unit.
I gather from reading the various threads on the Pelican site that the blue Bosch coil might not be the best choice. Perma Tune says the stock coil, being the black one for an 83 911SC, or any good 12 volt coil will work. My spare silver 944S coil was for a high capacity DME ignition so I was thinking it would be a better coil than the stock SC coil which is also much smaller. And it is new and test correctly , so seems like the best option.
My confusion is with the test result on my SC coil. I read a thread from someone with a high energy after market ignition system and he stated that his coil was low resistance on the secondary side which led me to wonder if the 70 ohms of the black SC coil was indeed correct for the Bosch ignition system but not the ideal for the Perma Tune.
I suppose I represent the notion that a little knowledge can be frustrating.
So, I was looking for an answer something like: "The SC coil is low resistance on the secondary side." or "the SC coil should be the same as any other Bosch coil."
I have specs from my old BMW motorcycle that are lower and spec from an auto coil that want 10,000 ohms. Big differences.
Anyway, I have posted the question at Pelican as well , and hopefully Warren the S man will find time to make a short reply.
I am inclined to dump the old coil and install the new coil I have.

Al Cody

Back to my theory that a little knowledge is dangerous. It would appear that I am misreading my ohms scales. The SC coil should be 700 not 70.
Ooops.
Back to all is good.
thanks Al C