[DAK]

Last week driving to work I noticed the voltmeter on my '94 Coupe pegged high, no secondary indications of trouble. Since my battery was from 2007 I went ahead and replaced it, but that had no effect on the voltmeter. As soon as I turn the key on, the needle leaps to the top of the scale. Any ideas on how I can troubleshoot and fix it?

 

Partial Post: Please Login or Register to read the full post.

[jfrahm]

If the car is running when the voltage is pegged, then it is probably the voltage regulator.  This can be replaced without removing the alternator from the car, but it is not easy unless you are used to the contortions and working by feel.  Also make sure you have the cooling duct in place as the lack of this part is very hard on the voltage regulator.

 

If it pegs with the key on, engine not running, then I suppose you have a problem with your gauge cluster.

 

-Joel.

Partial Post: Please Login or Register to read the full post.

[blau]

If the car is running when the voltage is pegged, then it is probably the voltage regulator.  This can be replaced without removing the alternator from the car, but it is not easy unless you are used to the contortions and working by feel.  Also make sure you have the cooling duct in place as the lack of this part is very hard on the voltage regulator.

 

If it pegs with the key on, engine not running, then I suppose you have a problem with your gauge cluster.

 

-Joel.

 

x2. Had the same voltage regulator problem on my Audi - read normal with key on/engine off, pegged with engine on.

Partial Post: Please Login or Register to read the full post.

[DAK]

It pegs when the key is turned on, before the engine is started. I've had the gauge cluster out several times over the years to fix the odo gears (twice) and the lights (3x), maybe that was too many jolts on the gauge. New gauge is about $500, looks like its gonna stay pegged for a while. 

Partial Post: Please Login or Register to read the full post.

[jfrahm]

I do not think the trimpot has enough authority to peg the gauge at 12.5 volts but you could see if maybe cleaning it would help.  It should be no big deal to replace a voltmeter with one from another cluster if that is what is needed.  Maybe it has mechanically failed so any voltage sends it off the scale rather than having progressive resistance to needle travel.  I think they use a little clockspring which could break or pop off or something.

 

I have had to replace a tacho in a 928 and it was not difficult and cluster parts were not expensive.  I do not think the voltmeter is a common failure so probably easy to come by.  That being said...

 

Please do check the system voltage, I could see blowing up the voltmeter as an early symptom of a high system voltage (when running).  In my case when my regulator died I could hear the HVAC blower running kinda fast also and changing speed with RPM (and a high reading on the voltmeter).  No Central Warning light though.  

Partial Post: Please Login or Register to read the full post.