911 sc tach dropping to zero then no start

[JBO]

Recently tach on my sc would occasionally start fluctuating wildly and/or drop to zero. No alternator light and car would continue to run, but when turned off sometimes would not start until it cooled off, then would restart fine and might run several times later with no problem. Took it to highly recommended local shop in Atl., and they said charging system was checking out fine and car was starting fine (though it had the problem when I drove it in, and in fact had to jump it off that day to get there). They did a tune up/valve adjustment and sent me on my way, unable to "replicate the problem". Of course I replicated it within 5 miles after leaving the shop, but it was Late Friday and I did not have time to go back. They must not have even road tested the car. Aside from the tach problem, the car is running worse - bucking and hesitating. Seems to be set to lean and starving for fuel. They also said my muffler strap was missing and charged me $69 for one without telling me! Even worse, I take a look when I get home and I have the same muffler strap I put on years ago when I installed a GHL muffler! In addition, I told them I only had around 1k miles on synthetic oil, so not to drain the tank and just top it off, and they said OK. Of course the invoice shows 11 qts of Valvoline 20/50 at 4.59/qt. Anyway, I'm just venting on all that. My question is this - they said if the problem continues they think it is the Permatune CDI box, and the next thing would be to replace that. Does that make sense to you guys? As you might guess I'm not trusting these folks and would rather just get my $69 back and not deal with them anymore. Very dissappointing, as they have been around 25 yrs and I had considered using them many times before but never did.

[Flat6pac]

I would look at theCD box because it is the tach drive and a permatune is always questionable
Bruce

[James Brown]

Sounds like the permatune death spiral. Remove and replace that unit with a MSD or Bosch unit ASAP.
Sorry about the highly recommended shop, did you sign a work authorization? Anyway, tell them of your ordeal and see if they fix it.

[boyt911sc]

JBO,

You need to know well about electronics to troubleshoot a CDI like Bosch or Permatune. But for those of us who are non-electronic savvy, I test my CDI by switching to a known working unit. Since I have some spare units at home, I simply replace a questionale CDI unit with another one and test. If a replacement unit solves the problem, you could safely assume that the old CDI is defective and would need some repair.


Borrow a CDI unit from some one and do the plug and test method. This is the easiest and convenient way I know how to test a CDI unit in the car. Having extra CDI units compensates for my lack of electronic knowhow in troubleshooting this problem. Keep us posted.

Tony

[Bob Kontak]

Originally Posted by James Brown

did you sign a work authorization? Anyway, tell them of your ordeal and see if they fix it.

James always says it better than I would.

+1 on ditching the Permatune. MSD is pretty reliable and easier on the pocket than Bosch.

Check your lights at night at a stop sign. Are they flickering? Could be the voltage regulator is tired and that can cause tach issues. I know the shop said the charging system is ok. Look for the flickering anyway.


Also, for grins, buy a $50-$60 multi-meter and start reading about some of the tests you can do on your car yourself. When you get your $69 back you will have enough for one. Good luck!

[ischmitz]

Permantune CDI boxes unfortunately have a less than stellar reputation and do fail quite a bit. Bosch CDI are much more reliable given that their average age is more than 30 years. If they fail its mostly due to an overvoltage situation caused by bad voltage regulators.

I would try and get a used Bosch unit to replace the Permatune. If the Bosch unit fails it can be repaired while some of the Permatune are potted with epoxy and thus non-servicable. MSD seem to work as well but I don't like that you have to splice into the Porsche harness. I like to keep things stock.

Ingo