No Power on Ignition Coil

[Jaggi]

I own a 1987 Porsche 930 and my car has stopped firing after I was working on my convertible top motor. I have diagnosed no power at the ignition coil when cranking and have checked all fuses. I cannot find anything wrong with the wiring harness or the connectors as well.
What other steps should I go thru to detect the problem? I appreciate your feedback.

[ischmitz]

If I am not totally mistaken the 930 uses a Bosch CDI ignition identical to the 911SC. Some 930 use the elusive Bosch 8-pin box but most use the 6-pin box from the SC. There is a magnetic pickup in the distributor that triggers the CDI box to produce a spark. You won't measure +12V power at the coil. This ignition system is very different from a traditional Kettering setup. The coil is used as a transformer and the primary voltage is around 400V DC. So please be careful when working on this system.

Do you hear the characteristic whine when you turn the ignition ON but don't yet crank? You need to open the hood and listen close to the left drivers side of the engine bay. The 6-pin ignition box looks like this:



If you hear the whine you confirm the ignition box gets power. Only the 6-pin box whines while the 8-pin boxes don't.

Check the green trigger wire from the distributor. It is a COAX cable and often is damaged from exposure to heat.

Regards,
Ingo

[Jaggi]

Thanks for your reply. I cannot hear a sound from the CDI in the engine compartment but it is very packed in the engine compartment under the air cooler. I see the CDI but have a hard time to reach it.

I tried this morning to start the car and it fired right up. (Couldn't get it to do anything yesterday). The only change I have done since then was moving my hand brake lever (I have a convertible with electrical top) and putting the key in and out of the steering lock. Before I tried to crank the starter I have checked the coil for 12V on terminal 15 or 4 with the ignition switch on run. No power could be detected. Shouldn't I measure 12V on terminal 15 while the steering lock is on run?

Then I started the car and as mentioned it fired right up. While the engine is running I can measure 12V on terminal 15 but it goes away when I stop the engine.

Now I lose trust in the car as I don't want to get stranded somewhere.
Might it be the ignition switch? Other ideas what to do?
Thanks again for your help.

[T77911S]

you have diagnosed wrong.

go back to where you were working on the to the top motor and see if you bumped something. perhaps a fuse, like to the fuel pumps or something like that.

next time it will not start, get a spare spark plug and connect it to one of theplug wires, ground it and check for spark while cranking.

[ischmitz]

Originally Posted by Jaggi

Thanks for your reply. I cannot hear a sound from the CDI in the engine compartment but it is very packed in the engine compartment under the air cooler. I see the CDI but have a hard time to reach it.

Do you have an 8-pin or 6-pin box?

I tried this morning to start the car and it fired right up. (Couldn't get it to do anything yesterday). The only change I have done since then was moving my hand brake lever (I have a convertible with electrical top) and putting the key in and out of the steering lock. Before I tried to crank the starter I have checked the coil for 12V on terminal 15 or 4 with the ignition switch on run. No power could be detected. Shouldn't I measure 12V on terminal 15 while the steering lock is on run?

Maybe I didn't make it clear in the previous post: NO - there will not be 12V ever on either of the primary terminals of the ignition coil. One terminal is GND and the other is a 400V pulse from the ignition box. Unless your car is modified you have a CDI system (capacitive discharge ignition). The coil is actually a transformer in your setup. The CDI box will produce a 400V pulse through the primary of the coil and that get transformed to about 40kV in the secondary and releases the spark.

Then I started the car and as mentioned it fired right up. While the engine is running I can measure 12V on terminal 15 but it goes away when I stop the engine.

This is impossible. Your volt meter might average the voltage over time and suggest you see something close to 12V DC. In reality see is a complex waveform.

Now I lose trust in the car as I don't want to get stranded somewhere.
Might it be the ignition switch? Other ideas what to do?
Thanks again for your help.

From your description your ignition switch might be intermittent. The electrical part can be swapped out and that is what I would do next.

[agentx]

my 1982 930 Turbo 3.3L has a Permatune Electronic ignition box in it that "seems" to test out ok by the steps they have online, but the big problem remains we are not getting power to the coil.. I do not have a wire diagram for the car... can anyone help?