Advice, finding problem burnt coil 911s 1969

[frankmar]

Hello,

I was driving along at low RPMs, the engine still cold and the car stopped. I tried to start it again with no luck. Looking for the problem, we first found that the coil was burnt. We tried a new coil that we know works and the problem persisted. My mechanic thinks the Bosch 3-pin module is causing the problem. Somebody else mentioned that the "Ballast resistor" could also be the problem. I am afraid to replace the module (This is expensive) and burn something again. Anything else I should try?

Thanks!

[beh911]

Are you sure you have the proper coil for a CDI car? Meaning the short/stubby transformer coil for this type of ignition system

[edmayo]

There is no ballast resistor used in the Bosch C.D. circuit. What was the evidence that the first coil was burnt? Are you saying that the second burnt also? Are you using the correct Bosch coil for the CD system? Systems Consulting can rebuild the Bosch C.D. units for a very fair price.

[304065]

Where, precisely, is the coil burned? At the tower? A photo would help.

You are getting advice from people who are not familiar with the ignition system-- as Ed says, there is no ballast resistor with a CD system. Post a photo of what you've got along with the part number on the bottom of the coil and we can take a crack at solving this issue.

[frankmar]

I have the correct coil Bosch 0221121001 the short/stubby one. Let's see if I can later post a picture of the burnt coil, that had the same serial number. In the picture I am posting you can see the "Ballast Resistor" y believe is the silver round piece that is also a Bosch part. The Porsche part number is 901 602 601 00 . The car's serial number is 119301031. I have the CD 3 pin Bosch box.

[304065]

That is the "intermediate unit" seach here for the words "einbau senkrecht" for more information. Anyway, nice original '69 panel, rarely seen in that condition.

[frankmar]

Thanks! This car is in amazing contition, and has nice extras like 100l tank, LSD and sport seats, 6851 silver. Now I hope I get it to start again :-) I am adding a picture of the burnt coil.

[edmayo]

I have NEVER seen a coil do that! Have you checked the distributor cap and rotor for excessive gap, spark plug gap? Its like there is a problem downstream from the coil causing the coil to have to build up excessive voltage to jump the gap. Did the coil have the heavy gauge ground wire grounded to the coil bracket? I don't have a ready answer for you, hopefully John Kramer might jump in here. He is Mr. Wizard with electronics!

[304065]

That looks like a Brazilian-made silver coil. These are notoriously unreliable. I was thinking that if the tower was burned up, it was due to a loose lead, but this looks like the coil windings shorted internally, and that then caused it.

[frankmar]

We have tried a new coil that we know s good, and still no luck. We are suspecting the 3 pin Bosh module... Is there anything else we can try? Any other troubleshooting tips? Thanks!