On my 1987 944 turbo when I hook a voltage meter up to the battery is shows around 12.20 or 12.40 with the car off. When I turn on the ignition is drops a little but stays above or at 12 volts. When I crank the car it register right at or below 12 volts. Upon reving the engine even to as little as 1400 RPMS it goes to 14.2 or so like it should and the needle in the car registers right in the middle of the gauge.

What I've done so far is

1. put a new voltage regulator on
2. tried three different used alternators - at least one out of a car that did not exhibit the same issues.
3. put the positive and negative cables on from an 11k mile parts car
4. cleaned the grounds under the cluster
5. cleaned the ground in the battery box and on the bell housing
6. cleaned the grounds at the front of the car before the headlights
7. swapped a couple different starters on
8. installed a brand new battery

When I start the car and have the low voltage reading I tried running a second ground wire directly from the battery to the block and that made no difference.

 

It sounds normal to me? How low does it drop when you crank it? It should be in the 11's, depending on how cold it is outside and what oil you're using.

 

Might be but I think normal is that once you start the car it should register 14 volts plus without needing to rev the engine at all.

 

You could try cleaning up the alternator cable connections at the alt and starter and/or replacing the alt cable.

jmd_forest

 

usually the gauge should read in the 13 range until you rev it- what does it read w/ all accesories turned on? Turn on the lights, radio and a/c or something and see if it goes below 12. Is the harness for the alt. in good shape?

 

Your alternator might not be working properly if you are getting higher voltage only when reving the car.
Btw, did you get my PM regarding eccentric camber bolts?

 

Just seems like all the other 944s I've been around - when started the voltage gauge goes to the middle of the range without any initial revs. Harness for the alt. is in good shape with no issues.

I do have an ICEshark kit that Albert is offering to sell me - maybe I should install that and see what happens....

 

Any other ideas?

 

You in the garage today? I'm bored

 

I wish - sitting here at work surfing OT.

 

Your alarm is only partially bypassed, so the field voltage is never applied. If you rev the car, the alternator auto-excites.

There is another pair of pins you need to bridge to fix this - search and you should find it. Someone else had this answer a year back or so, and it fixed his. I haven't gotten around to doing it yet.

 

I'm not finding the post....but check that both of these are jumpered:
http://www.clarks-garage.com/shop-manual/elect-23.htm

And make sure your alternator light is good in the console. I know it sounds stupid - but it's part of the charging circuit. If the bulb is out, you'll never get field current (D+ on the back of the alternator).

 

It shouldn't read 14v until about 3k rpms.

 

When I made the switch from a road car to track car I created this same symptom. A friend told me that taking the factory tach out of the picture loses the signal to the regulator. At an RPM higher than idle, the alternator auto-excites. Mine does it now at 3k. Its a Bosch alternator thing.

 

....if you aren't powering D+ (field current). A properly sorted car will put voltage to D+ on start, and you will see voltage from the alternator with no revving necessary.

This isn't just a typical 944 issue, it's a typical auto issue. It's just more common to see on 944s because some ridiculous 1980s German logic said you should run this not only through the alarm, but also through a plug near the brake booster, either of which is likely to be bad by now.

The dash light being part of this circuit is completely typical on cars of this era, and is the most likely cause of this EXACT issue on everything else of the time.