3.2 alternator woes

Ohio911 · 09:41 AM

Recently my 73 911t 3.2 conversion has been acting up. I had all of the symptoms of a bad alternator. I tested with voltage meters and was seeing 12.6 at the most while the car was running. If I turned on the lights while it was running It would drop down to like 12.0 or even 11.9 volts. Could this be a bad battery since it goes under 12 volts? Weirdly enought it has plenty of cranking power and starts up everytime? Symptoms include bouncing tach, headlight lights getting brighter and dimmer as I accel or decel. Gauge lights doing the same and even the instrument readings are moving around a bit and most recently it has come to the point where the car surges once it is warmed up. I did here the infamous squeaking that most people seem to relate to a bad belt or alternator. This brings me to the main question. I have a brand new voltage regulator and it appears to be doing it's job. No jumping to extremely high volatges.

My 3.2 engine is from a 85 911 and the car is a 73. My engine was originally going to be a turbo engine but the previous owner whom had it built changed his mind at the last minute. So the Builder made it a 3.2 engine but the gear on the crank was reversed so I have to use a bosch cdi box for my spark signal and a late 70's distributor probably like what was used in the turbo. What alternator should I have in my car. I noticed that the 84-88 3.2 cars seem to have a higher amperage alternator in them. Is this because the computer and all require more amps? Do I need a more powerfull alternator then tyhe 70n amp marchal I have in there? Sorry this turned out to be so long. Thanks for any help!!

Thrasher · Thrasher's Garage

I'll leave this one to the resident alternator experts. I did have issues with my 3.2 alternator and got loads of help on this board. Mine was a bad regulator and worn slip rings, though.

I think that you'll need to specify whether you do indeed have the 3.2's bigger alternator with the internal regulator or just a 70 amp alternator using an external.

Other things to rule out first:

fan belt - if yours is slipping, the loaded alternator could cause it to slip even more, resulting in a lower voltage output.
battery - take it to a local shop and have them do a load test. These tests are usually free of charge (no pun intended)
ground(s) - make sure your ground points are clean - esp the big strap to the transmission.
voltage drop - do a search on that term and do the test. It will require only a voltmeter - buy a cheapy at Harbor Freight or similar if you won't be using it often.

IIRC, sure the DME and other electrically operated devices (essential to 3.2 operation) add some load, but accessories found on Carerras, like A/C, stereo amps, fog lamps, etc. require more amperage than early cars would've been able to provide and that was really the driver for a larger alternator.

ZOA NOM · ZOA NOM's Garage

The brushes inside the alternator could be worn.

Wil Ferch · 04-06-2006, 10:17 AM

All good info..but start with the basics.

A fully charged battery ( standby..car "off") is 12.6 volts. Anything under 12 V or high 11's is ...for the most part ... a "dead" battery. Yes... the slope is THAT fast !

At 2000-3000 RPM...you should be seeing 13.8-14.5 V.....less is probably a bad alternator....more is probably a bad voltage regulator.

Start with this...go from there....

Wil

Huh · 04-06-2006, 11:02 AM

I have been having alternator problems on a non P-car (VWs) but an alternator is good if above about 13.3V to 14.7V. With lights and other accessories your the alternator should drop down to about 12.6 or a bit higher but when you run it above 2000rpms is should go back up to about 13.3v. Voltage regulars are the best start. You should try checking at the battery terminals first for voltage then put your meter positive on the positive output on the alternator and the negative lead on the negative terminal of the battery. That will tell you your actual alternator output.

Ohio911 · 04-06-2006, 11:08 AM

Thanks for all the great info. Yes I am currently running the Marchal 70 amp externally regulated alternator. I will try these suggestions tonight and post my findings tomorrow. God bless the internet!!!!

FrayAdjacent911 · 04-06-2006, 11:12 AM

My alt was having problems when the engine was in my coupe. Made it from Midland, TX back to Austin TX on an alternator that was not charging the battery. Jpnovak took a look at it, cleaned it up a bit and resoldered a few connections, and now it works fine. I get up to about 14.5 volts at the battery, and all is well.

I might just need cleaning. It might need rebuilding.

Ohio911 · 04-06-2006, 11:20 AM

Does anyone know where one would take the alternator to in order to have it rebuilt? The closer to ohio The better : ) Thanks

Huh · 04-06-2006, 12:00 PM

Check some of you local alternator shops. Find out how long they have been in business and as for some references if you are a bit leary. We have one in Indy that rebuilds but it is $28.50 just to crack the case then parts. It comes out to about $70-80 for a 90amp Bosch.

Ohio911 · 04-06-2006, 12:03 PM

Thanks for the info.

100 bucks would be a small price to pay to get my car healthy again. I might do just that.

Thrasher · Thrasher's Garage

Do I hear Loren stepping up to lecture on "you get what you pay for" with alternator rebuilds?

Caveat Emptor.

Joeaksa · 04-06-2006, 12:51 PM

Quote:

Originally posted by Thrasher
Do I hear Loren stepping up to lecture on "you get what you pay for" with alternator rebuilds?

Caveat Emptor.

An alternator is not black magic. I had the one in my 3.2 overhauled at a local "mom and pop" shop for $75 many years ago. It worked fine for another 4 years until I sold the engine to upgrade to a 3.6.

Personally I could care less about Loran and his rants. He had a lot of credit on this forum until it was brought out on the forum that he was going after SW and his chips, THEN it became known that he was also selling chips.

Get your alternator tested and overhauled if necessary. No need to send it to a specialist, just a good local shop. I did not even tell the people it was for a Porsche and he had parts in stock for it.

JoeA

Huh · 04-06-2006, 02:37 PM

I agree that just because you get something fixed inexpensively it will be crap. I know a mechanic who is as good as the most expensive guys out there. He charges $65/hr and when he quotes something and he does it in less time he charges for the time spent on the car. He believes that he will build more business and retain more customers being fair. I would put his work up against any of the higher priced guys.