alternator expert need help

[ertech]

Hi guys .
my car a a 89 Had my tach go wild once in a while but never has anything to measure voltage when that happens.Had my voltmeter in the car and this time was able to measure the voltage . it was at 11.4 and no mater how much I reved the voltage would not go past 11.7. it I turn off the car and let it cool .when I start again get 13 while running at any RPM.
1-why would My alternator light not come on when this happens?
2-I can change the voltage regulator easily but what if it a diode problem what do I do?and is there a way to check this?

Thanks

[A930Rocket]

Sounds like a flaky alternator or maybe a loose wire. check all your wuring first, including the connections at the starter. Rather than trying ti rebuild it, I'd replace the voltage regulator or the entire alternator preferably (as long as your in there). A new alternator would be the first choice and a rebuilt one second choice.

[Schwarzeritter]

I have to agree with Rocket, deffinitly go with a new alternator.
I did once go with a alternator rebuilt by Bosch and that one has
served me well.

On things of a rear engine or mid engine nature I
never like risking with re-ferbished, or re-built.
Because the cost and timedown is a real pain for the replacement.

( Do! while you are in there inspect harness/looms
that be! ) On some of my own 911 variants I have made complete harnesses. Ofcourse my personal units exceed military grades.

Just remember, loose wire possibly free, fresh brand spanking new alternator ( not free, pricey. )

Good luck.

[totle]

My friends 89 930 had kind of same problem. after some driving, his tach went crazy, and then car stopped.
Sometimes it fried the fuse (position 1 I think).
After he changed the altenator, all was fine

[ertech]

Do not want to spend big $ for a new alt
And you are never shure of what is rebuilt in a rebuilt....
If I replace the regulator and bearings this should fix my problem?...
How do we know if we have a diode problem and why when all this happens why do the bat light not go on?
Thanks

[ayebaal]

If your alt. isn't making noise the bearings are probably ok.
Diodes are like a check valve, they let the current flow in one direction only. If they flow current in both or neather directions they are kaput. You can check this with a multi-meter.
There seems to be a number of different alts for your model year, some having the internal reg and others having the external. If I had the external I would be considering swapping out the the old reg. first.
The light didnt come on because it was still charging.