95C4VanIsle

I thought I would do a quick follow up on the possible alternator problem I had. I had the battery charged fully and reinstalled in the car. I went out on a drive last Wednesday with a wrench friend (helicopters but knowledgeable about cars) and after about 15 minutes the battery light started to come on. We drove the car home and tested the voltage and it had dropped to 12.2 so he felt it was probably the alternator. I was going on a trip to the East coast for 5 days so I put the car on trickle charge and it was at full charge on my return last night.

I drove the car 15 miles into the mechanic (mostly BMW's, Audi's, VW's) and no lights came on. The mechanic called late this morning and said the battery was fine and he wasn't noticing a drop in voltage with the car running but he would try it again later in the afternoon. He called back about 3 PM and said he had noticed a voltage drop after running the car for 15 minutes or so. The car was just idling in the shop.

He said he would pull the alternator in the next few days and order a replacement.

I hope that solves the problem. I'll post back when I find out.

Thanks to all of you for your help.

Garth S

FWIW, many alternators start dropping output due to worn carbon brushes .. others due to a dying regulator: both issues are covered by installing a new regulator/brush set: costs ~$35, and takes 2 min to swap once the alternator is removed.
Did this in mine ~2 years ago ...

briefescape

Hey Bret

I swap the alternator brushes in my cab and it also cost aprox. $40
No problem since .

Cheers Guy

95C4VanIsle

There is an alternator repair place in our town but they aren't used to working on Porsche cars. If the brushes can be replaced that would certainly be cheaper than the alternator replacement at $364 for a rebuilt alternator. I'll check with the alternator repair place. The problem might be that the mechanic will only warrany parts that he has sourced himself. I'll check with both today.

Thanks for the information Garth and Guy.

JeffC

I had the same symptom a couple of week including the radio going off, but they all went away and I continued to my destination and back home (about 10 miles total). A couple of days later, the car started but it didn't sound like it would crank again. I charged the battery and measured the static current draw with the car not running (~600mA) which is OK I believe. Car sat for a couple of more days and then it wouldn't start. Until this weekend, my schedule prevented me from doing any diagnosis. Turns out, the battery is not being charged. No change at all in the voltage at the battery. Some of you may know the engine was just reinstalled (SAI issue) so I have some questions.

Has anyone experienced and alternator that doesn't put out any voltage?

Since the motor was just worked on, is there a connector some place that may have worked itself loose and prevent the alternator from connecting to the battery?

Thanks for the help.

Jeff

Felix

600 mA is 14.4 Amp hours per day (0.6*24). A typical Porsche battery will be rated at 70-74 Ah - that means your current draw will kill a battery in 5 days. Something's not switched off when it should be - typical culprits are the glove box light and front compartment light. Could also be a stuck window relay - will your windows work with the ignition off and the doors shut?

Garth S

+1 .... just to add that a typical parasitic draw is ~35mA, so 600 is a real problem.
A failing diode in the alternator can cause this, but after doing the checks that phelix notes, the easiest approach is to pull the fuses one by one until the draw drops - with luck, you've found the problem circuit. ( the hot wire from the alt. needs to be removed to test it - and neither the alt nor starter are fun to get at, so go for the fuses first :0 )

Quadcammer

You can easily drive a car pretty far without an operating alternator. 50 miles should be no problem, especially on a car like a 993 which doesn't have the heavy electronic draw of something like an S-Class mercedes.

JeffC

Garth and Phelix,

I did the checks and when I got to fuse 11 (i did it backwards so it took me awhile) which is the Interior lights etc, the current draw went to near 0. Then a light came on (in my head), that I took the initial measurement with the hood up. duh! The under hood light is on so that is where my current draw was from. The car starts but the voltage at the battery is about 11.4 volts. So it looks like I am back at the alternator, would you agree?

Jeff

Garth S

Most likely the alternator ... but before declaring it dead, disconnect the battery and check the posts for corrosion/tightness - then either get a load test done (CCA - cold cranking amps, or % or rated capacity) or hook up a charger so as to be certain you do not have a dead cell - that can make a good alt. look bad
If the battery is OK, it is likely the regulator/brush set in the alt ....

Felix

A simple alternator test is to run the car at 2000 rpm with loads of electrical consumers switched on (high beams, interior fan, rear defroster etc) - at the battery you should see over 13V.

PS. You can switch off the front compartment light by depressing the catch of the latch - just be sure to pop it open again from inside the car when you want to shut the front lid!

JeffC

Previously, I had checked the battery voltage at a higher rpm and the voltage was at 11.0volts which led me to think alternator. The battery is on a charger now and will see what happens. I hope it is the battery but it was installed as new when the motor went back in.

JeffC

OK, hear is the scoop. The battery charged completely to 12.8 volts. The car started and at idle, the voltage at the battery was 12.5 volts. Increased the rpms and the voltage stayed at 12.5volts. Guess it is the alternator. Where can I get brushes and a regulator?

Garth S

Here's an ebay example - if you want a part stamped Bosch, search under the header link .... of from any site sponsor.

Felix

Try http://www.pelicanparts.com/catalog/..._pg1.htm#item3