Voltage Problem
 

I'm having a bit of a voltage problem on my 85.5 944. Car starts and runs, but only shows around 11 volts or so, goes up a bit at higher RPMs. Already replaced the voltage regulator, any ideas?

check the ground wire from the batt to the back of the engine for corrosion.
if it looks like it's been in a swamp replace it.

or the alternator itself might be in need of replacement.

Are you using the voltmeter in the dash to check that? If so, the reading may be inaccurate. There is a post in the tech section of this web site where a guy explains how to fix the inaccurate gauge reading problems of these cars. If you are using an external volt meter, there may be some ground issues to deal with as bearone2 suggested.

yeah I checked it with an external volt meter. 12.04 while the car is off, 11.92 while it's running. Since I already replaced the voltage regulator I assume it's the alternator

Not much else in the charging system, is there? These cars do have a problem with ground wires and it could also be the main battery cable as the alternator sends current to the starter which in turns feeds the battery I think. Usually if an alternator is charging, it's good and if it's not charging, it's not good. I would look at grounds and battery cables to make sure there isn't some bad connections first. You could also put an amp meter on the alternator main wire and see what the amount of amps it's putting out are. If it's putting out the amount of amps it's suppose to, the alternator is good and it's definitely a cable or connection somewhere. Hope this helps a little.

One mod that really helps is to drill a hole in the firewall/battery box and run a ground directly from battery negative to the engine. The intake runner bolts are as good a place as any to attach it to. And make sure to insert a grommet into your freshly-drilled hole.

HTH

the hole's already there.

thats where the ground cable runs from the neg side of the batt to the back of the engine.

Just noticed where you are from....might have to come over and check out that problem personally! Sounds like your ground is in the right place. You may want to check your voltage on the main starter wire (I know it's a pain to get to, but clip on a wire with an insulated alligator clip before you start it) and see if you have the right voltage there. If it has the right voltage there but not the battery, change the positive side battery cable. Let us know what you find. Does your battery stay charged?

Does your "charge" instrument light work? If not replace it. It is part of the circuit. You need at least two volts at the blue wire to set up the field current in order for the... er... alternator to alternate.

charge instument light? I assume you mean the idiot light for the voltage gauge. Yes, that comes on, and then fades out as revs go up.

Yes, the idiot light for the voltage gauge. Does it light during idle, fade with rev up, and light back up at idle?
Is the belt slipping?
Does the alternator have a good ground?
Did you check the voltage at the starter terminal? If it's still low I'm afraid it's a bad alternator.

I would definitely check the belt for tension first, then look at grounds. The other thing I would do is take the alternator off and take it to my local parts store and have it checked if I don't have an amp meter myself. Here, they check them for free and that should remove all doubt for you without any expense. They should also check your regulator for you as well. I'm guessing that one of the two are not grounded well or the belt is the problem. My first guess is the belt.

yeah that's exactly what the light does. The belt is brand new and was tensioned by the porsche mechanic when they did the belts a week ago. The car has been sitting for a couple years so I'm not surprised there's a couple problems in the electrics. I haven't checked the voltage at the starter terminal yet. I might just have the mechanic fix the problem when it's at the mechanic next week to trace down why the headlight motor sporadically works.

It would be best if you could put an amp meter on the alternator. If you don't have one, check with the auto parts place and see if they will test it for you. Save some money. Just a thought

yeah I've got a multimeter, just not a whole hell of a lot of time. Car's registration expires next month and they won't renew the registration without the emissions done, so everything needs to be ready asap. I've done 90% of the work on it and just need the rest done quick.

just heard back from the mechanic, it's definately a bad alternator. So there's $180 in parts.