Alternator/Voltage Regulator

[dskiles]

I just purchased a 1997 993 Targa (with 53,000 miles). Yesterday we drove it from Texas to Florida with no issues. This morning, it started right up (nothing like the sound of an air-cooled Porsche!)

Later in the morning, the starter struggled to turn over the engine with no success in starting it. I turned off everything (AC/radio/closed doors) and it was able to turn over enough to start the engine. Drove it a little and it happened again. Several times today I have been able to start it, when all electrical systems are off (all that I can turn off).

Figuring it was possibly the battery (which was installed in 2007), I took it to the local Auto Zone store. Tested 100%. They told me we need to check the alternator. They hooked up a meter to the battery and while the engine was running, their meter indicated a failed alternator and voltage regulator. They said it could be the voltage regulator causing the problem.

None of the warning lights come on when I am driving or starting the car.

I had a very thorough PPI done before purchase with new cam cover gaskets and a new power steering hose installed. None of these issues came up.

I am curious to know if any of you can lend some insight to this?

[KNS]

I'd agree with Auto Zone, you Alternator is shot, second choice would be the VR. If they are the same age and/or original to the car replace them both.

[911nut]

The voltage regulator is integral to the alternator. It could be failed or the diodes in the alternator could be failed. When you remove the alternator you can check the diodes with a mulitmeter just for fun but you might as well go ahead and replace the alternator. Installing/removing the alternator from the engine isn't a lot of fun and if you want to piecemeal the repair (replace the voltage regulator), you might end up doing this.

A genuine Bosch rebuilt alternator is $200-250. Try to source it locally as shipping alternators and cores to and from Cali adds another $100 to the bill. Replace the fan and alternator belts while your in there.

[dskiles]

Thanks to both for your input.

Do alternators slowly fail over time or fail suddenly?

What happens to the car if they completely stop working? I.e., is there any danger to the rest of the car by trying to get a few more miles out of it?

[briefescape]

If alternator is not working properly it will eventually drain the battery and your engine will quit ( usually in the most inconvenient place and time , for example at a major intersection on the way to an important meeting )

Sorry but before you replace the alternator there are things you need to check , you say the alternator warning light does not come on . I would first check the ground wire to the starter and make sure it is grounded properly ( this a very common issue with 993s )

Auto Zone voltage meter reading does not tell you your alternator failed , it reads the voltage period . They did not share what the voltage meter read ? It should read between 14 and 14.2 volts .

The alternator may just need new brushes or it could be the flimsy contact point from the voltage regulator to the alternator ( which is a matter of just pulling the copper connector up with your finger ).

Unless the shaft is not turning freely ( bent shaft or worn bearings ) on the alternator
I would not replace alternator .

I am not a mechanic by any stretch of the imagination but I fix my own alternator with all the info here and Rennlist

Here is a link to DIY Pelican Technical Article: 993 Technical Article:

[911nut]

If your alternator is still installed, have someone hold the engine at 2000 rpm. Take a multimeter set to dc voltage and hold the probes on the battery terminals. You should read something on the order of 12.4-12.8 volts. If higher, replace the alternator. If lower, make sure that the alternator belt is not slipping and the battery terminals are clean. If those items are ok, replace the alternator.

[Traveller]

Originally Posted by 911nut

If your alternator is still installed, have someone hold the engine at 2000 rpm. Take a multimeter set to dc voltage and hold the probes on the battery terminals. You should read something on the order of 12.4-12.8 volts. If higher, replace the alternator.

The upper end of that range would be an acceptable OCV for a battery with the engine not running.

With the engine running, you want to see 14.0 to 14.4V at the battery terminals at 25C/77F; slightly more in the order of a few tenths of a volt on a cold day and slightly less on a hot day.

This is with the engine running...

[wesleyc]

53k miles on one of these alts seems a bit premature for failure. At 113k I had a similar problem on my 95. No alt light yet the auto parts store meter showed good brushes/ bad alternator/ good battery. The engine cooling fan seemed to stay on too long so I put in new relay/ballast resistor/temp sensor. Still stayed on to long I thought ? I put in a new alt from pelican. Battery still draining. Put in new higher amp battery. ( just for ****s and giggles at this point ? ) still drained battery. In the end alt. regulator. Battery. Engine cooling fan stuff was all good. My problem was a incorrect plug plugged into the temp sensor receptical making my fan come on high speed way to long after parking this caused the battery to drain whilst running around in town. Plugged in the correct plug. No problems... Your car has the newer style fan so I'm sure this is probably not your problem. And I don't want to confuse this thread. Just saying my confidence in my local auto parts store and me not analyzing things better sent me on a wild goose chase when they said I had a bad alternator ?

[KNS]

wesleyc,

Glad you figured out your problem! You're saying that a completely different plug was connected at the temp sensor (in the air duct)? Was the correct plug simply laying nearby or tucked away/hidden?

[dskiles]

Well, I decided on the "doing nothing" option and so far this week, everything has been OK, although I still take the precaution of turning off all electronics before starting the car. Yesterday it was a little sluggish turning over, and today back to fine.

I talked to a local Porsche mechanic and he said that he will look for loose connections next week when is doing some suspension work on the car. He thinks it could be something loose in the wiring.

The responses on this forum were great. Thanks to all.

[wesleyc]

Yes KNS. That's what happened. 95 mods with old style cooling fans and updated wiring harnesses have a couple extra unused plugs. One which works but tells the fan to come on high way too often. It wasn't a problem till I had my first summer in the car ( ac on a lot ) not dskiles problem with his car. I'm just saying a guy at the auto parts stores word and diagnosis might not be correct ? On the upside I do have a bunch of new stuff on my car now.

[KNS]

wesleyc,

My car has the updated wiring harness and I had noticed that there are a couple of unused plugs. My fan hardly comes on at all in very hot weather (unless I'm using interior heat). I think my issue is different than yours...

[wesleyc]

KNS my fan is slow to come on also now the the correct plug is in. Even with the new components the fan tends to have a mind of its own when to run or not ?

[KNS]

Maddening.