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911 charging problem help with diagnosis

Hi, I have a 1986 911 and the charging is weak at about 13 volts or so on my hand held meter.Any way to determine if it is the alternator or the voltage regulator. Thank you.

Old 01-08-2008, 03:00 AM
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Tons of stuff if you use the "search this forum" feature..
Here is a very recent one.
Symptom/Solution – Bouncing/Floating/Off Tachometer and Random Bulb Burnout.
Hope you find what you need...
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And I sold a bunch of parts I hadn't installed yet.
Old 01-08-2008, 04:21 AM
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911 charging problem help with diagnosis

In my 1986 911 3.2 the question I have is. How to isolate the voltage regulator from the alternator.And to accurately determine which is not working properly.It is undercharging.Thank you.
Old 01-08-2008, 09:16 AM
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How old is your battery?

Reason: a bad or low battery will trick you into thinking your alternator or regulator is bad.

Here's the scenario: you just spent the moolah on a new alternator along with a new regulator only to find out is still isn't charging right and now you just found out your battery was bad.

Imagine how I stupid I felt when I did that!

Last edited by stlrj; 01-08-2008 at 12:16 PM..
Old 01-08-2008, 09:23 AM
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I agree with the 'check your battery' advice. I went through this with my 85 one year ago. Had the alt rebuilt even though it bench-tested OK, had a new VR installed, cleaned all the connections, grounds, etc., re-installed the group 49 monster battery, all for naught - the charging problem went away when I installed a red-top Optima.
Added bonus, now I don't have to check/clean out battery acid overflow in the front.
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Old 01-08-2008, 01:51 PM
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STEP ONE ...... check standby voltage of battery.. car "off".

12.6 v = 100% charged
12.4V= 75%
12.2V= 50%
12.0V= 25%
under 12V= essentially a dead battery...or close

Yes..it drops off that fast as an indicator of charge/condition.
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Old 01-08-2008, 02:01 PM
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911 charging problem diagnosis.

Thanks Guys,
I posted here to get ideas.I put a VR in my last 86 myself and wanted to be sure.I did remove the battery and charged it and it is weak.Thank you for all your help.I will post another question as to where is the best place to buy tires (I checked tire rack).And what is recommended/preferred brand for street use.
Thanks again.
Old 01-08-2008, 02:02 PM
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Quote:
Originally Posted by keyla View Post
Hi, I have a 1986 911 and the charging is weak at about 13 volts or so on my hand held meter.Any way to determine if it is the alternator or the voltage regulator. Thank you.
I have a similar problem on my 1970 911T (two batteries) ...

After a 2 months storage, I foud my batteries down (watch, alarm ...). I charged them with an Accumate (soft charging system) and they reached 13.6V without any problem after 3-4 days.

When Accumate disconnected, the batteries stay around 12.5V

When I started the 911, I mesured voltage and found it was moving from 14, 15 or 16 volts with no direct relation with the engine RPM.

I changed the voltage regulator for a new one (901-603-206-02-M14) and when I started the car, the voltage is now perfectely stable but "only" 13.6V instead the usual 14.4/14.5 Volt

Any idea ?
Old 01-16-2008, 01:10 PM
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I am unsure.I would run a new thread and see if you can get advise.
Best wishes.

Old 01-16-2008, 01:13 PM
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