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Not sure..Kiss method....see if you are cooking you coil..go from there
Old 09-28-2011, 01:04 PM
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My '78 Targa's engine would quit and I had to switch the ignition off, count to 5, and then it would restart. Turned out it was the rev limiter latching up due to voltage being too high. Replaced the alternator but by that time the CDI was toast, subject to over-heating at standard high engine compartment temperatures.
Old 09-29-2011, 07:33 AM
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Quote:
Originally Posted by 930cabman View Post
My 1975 911s has a similiar issue with a different twist. Generally when I start the car (cold engine, sitting for a day or more) the alternator light will come lit, sometimes faint, sometimes fully lit. After a short time the light will go out and happy motoring.

Every so often while running the tach will start bouncing around and often (not always) the engine will cut out (sometimes with a loud backfire aka Uncle Buck). I generally wait a sort time, 5 minutes or so, start the engine and we are back on the road again.

Question, are all these issues related?

Thanks
Yes, the SCR in the CDI is self-firing due to the alternator charging voltage voltage (not necessarily the battery voltage too) being too high, the tach bounces due to the extra firing pulses, sometimes the extra firing pulses are high enough to trip the engine rev limiter.....BANG!

The rev limiter locks up, also due to the high voltage, and you cannot restart the engine until the ignition is switched off for long enough to "unlatch" the rev limiter. In my case that was a slow count to 5.
Old 09-29-2011, 07:40 AM
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Quote:
Originally Posted by wwest View Post
Yes, the SCR in the CDI is self-firing due to the alternator charging voltage voltage (not necessarily the battery voltage too) being too high, the tach bounces due to the extra firing pulses, sometimes the extra firing pulses are high enough to trip the engine rev limiter.....BANG!

The rev limiter locks up, also due to the high voltage, and you cannot restart the engine until the ignition is switched off for long enough to "unlatch" the rev limiter. In my case that was a slow count to 5.
Get an MSD vs. the stock CDI. My MSD just laughs at the overcharging voltages I see occasionally. Of course, it may not laugh forever....
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Old 09-29-2011, 10:40 AM
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