4000rpm on starter!

[billjam]

It looks like the electrical gremlins are at work in my 930.
I recently replaced a dead PermaTune CDI with a Bosch unit. At the same time, I checked out all the wiring (including the dreaded green one) and the voltage regulator and couldn't find any problems that might have fried the CDI, but in the two weeks since then, the car has started running very roughly when cold and when I crank the engine, the tacho reads 3-4000 revs

When it is warmed up, it runs fine and is still really strong on boost. Keep in mind that "cold" here is about 20*C, not F.

I am going to launch into this today to try and find the problem, but any hints would be appreciated.
Surely someone out there can join the dots for me:

• tacho reads 4000 when cranking (but stable otherwise)
• very rough running when cold
• plenty of power once boost comes in
• AFRs when running rough are 13-14 (I would have expected much lower if ignition is misfiring)

[Speedy Squirrel]

6 pin Bosch or 5 pin Bosch?

[billjam]

CDI is Bosch 6 pin.
I would like to test it but can't find test procedure. My 930 manual shows some sketchy details of testing an 8 pin unit, but no mention of 6 pin.

Permatune have this on their website. I presume the Bosch unit should be similar, but does anyone have specific test procedure for Bosch CDI?

[Speedy Squirrel]

Start with a wiring and coil check. Here is what I have for the Bosch unit. It seems that the distributor green wire is reversed on the Bosch unit compared to the Perma-tune. What do you think?

Here is what I have for the Bosch CD Box, using the numbering in your note (looking into the box connector):

1. (brown/white), system ground, coil pin B (31/1)
2. (black/violet), tach signal (TO)
3. (green wire shield), distributor pin A (31/d)
4. (white), coil pin B (A)
5. (red/white), coil pin A (15)
6. (green wire center), distributor pin B (7)

For the stock Bosch ignition coil, resistance between terminals A and B should be very low 0.1 to 0.165ohms. Terminal 4 to A should be 390 to 630 ohms.

Don't crank the vehicle with the coil secondary disconnected!

[billjam]

I wrote the equivalent terminal numbers on my wiring diagram at home so I can't confirm right now, but the Bosch and PermaTune CDIs are directly interchangeable with same connector on both, so there shouldn't be any difference.
Thanks for coil specs. I'll check that tonight.

Still looking for test specs for Bosch CDI.

[brooklynNY]

What was the reason of 4000rpm on starter. My car 1980 911sc row lost spart and does not start. I hear whining after ignition
Ideas?
I have 4000rpm on starter

[T77911S]

is the bosch unit used or rebuilt or verified it works? could be the ignition part is good but tach output is bad.

you might check control pressures/sys pressure.
air leaks.

is it rough at idle only or when driving
voltage reg. how did you check it. multi meter on battery?
did you check AC ripple at batt
is the alt light on with key on engine off.
did you change coil and CD or just CD?

i think i have seen this problem here, try searching. i know its a pain weeding thru the crap.