erratic tach
 

need some help on my tach in my 87 930. worked fine yesterday, yet when i started this am (it was a freezing cold 45 in sunny so. fla) the tach was dead which has happened before only to work fine within a min. or two yet today it was all over the map. icecked voltage at the battery which was 13.6 . i tapped the tach with fingers and it moved. could this be a loose ground behind tach? i checked other ground spots ...thanks guys

Does sound like a loose ground. Other's have had similar problems and it seems that usually the alternator is the issue with low output. But your battery voltage doesn't seem to support that as the probable cause. Check grounds regardless.

thanks mark i'll try all grounds

It's a dodgy diode in the alternator i'm told, can't be replaced either so you'll need a new alternator. That's if it isn't a bad ground of course :)

funky tach
 

I have had a similar issue with the tach on my 1987 930. Every so often, maybe once a month, the tach will read 5,000 and fluctuate when the engine is at idle. it has behaved in this fashion since I owned the car, about 18 months. I will shut down the engine and restart, generally will correct. The charging system appears ok, never an issue with low battery, possible a weak ground or other internal electrical gremlin.
John G

Alternator, and you could rebuild it for around $100.

when it happened to me it was my alternator.. best test... cut on the radio and the headlamps and see if it is able to run for very long.. if its the alternator.. it died in just a few min..

ok well after i got home from work ( the temp. outside had risen to 65) i started the car and everything was now ok. did a psuedo load test with everyyhing on and still had 13.6 volts. thanks for the feedback guys. i just find it strange that its happened only once before also on a cooler day. glad this particular 930 is in so. fla!!! thanks again

While you are checking grounds, check the pos connection at the starter. The alternator wire runs through there to the battery. Found out the hard way my alternator wasn't bad after I replaced it and still had problems...

Those cold days generate extra strain on the electrical system. It might go away while warmer; but then next winter... Be sure all is OK. M2c.