Alternator issues.......again

[Jamey]

I had my alternator for my '82 911SC rebuilt about 1 1/2yrs ago at a local shop. I also replaced the starter and battery about 6 months ago. With that being said, here's my problem-- Until yesterday morning the car had been running great. I notice that the alternator light flickered a couple of times right after I started her up. Just a couple of quick flickers upon startup and once more as I was slowing down for a stopsign. I read through the archives on this topic but couldn't find anything that matched my problem. After checking the car with a digital tester here's what I have:

1. battery has 11.8V with engine off.
2. battery has 11.3V with engine running at 1200 rpm(checked at battery terminals)
3. battery terminals are clean
4. battery ground strap and tranny ground strap are clean
5. 12 pin connector in engine compartment looks good
6. All connections on starter are clean and tight
7. Alternator light comes on as it should with key in "on" position
8. Alternator light doesn't glow at all with engine running. Just flickered a couple of times as mentioned before.
9. It looks like I have the original VR(located in driver side of engine compartment behind a plastic cover)

Obviously, I'm not getting a good output from my alternator, actually it would appear theres no output at all. The slight drop in volts when the engine is running probably is the radio and electronic ign. If my alternator or VR is bad why wouldn't the alternator light glow as designed? I can't afford to just start swapping parts out until I find the culprit so any thoughts would be greatly appreciated. TIA

Jamey

[Lorenfb]

The '82 SC had an internal regulator unless it's been converted to an '81 SC.

Things to check:

1. the B+ connection on the alt. S/B soldered
2. the alt. connections (2 each) @ starter also S/B soldered
3. the alt. connection at the battery

If above O.K., it's time check the alt.

1. worn slip rings/brushes
2. bad regulator

[Thack]

Do you have the updated internal VR? I didn't know mine did untill I had it rebuilt. Either way the PO had the old VR still connected! After the rebuild I disconnected it and the voltage went up to 14V.

[304065]

First, good job reading the archives, you started diagnosis with the right info. You're right, there's no output, and the bulb is only flickering.

An external reg on an internally reg'd year is kinda strange, but if you had good voltage before, let's focus on getting it back.

Revised- your bulb is glowing brightly.

If the bulb is going out, you have balanced output between the alt and the battery through the blue wire circuit, but no voltage at the battery. That suggests a helluva voltage drop from the alternator output terminal to the battery terminals. I would pull the alternator and clean the B+ terminals very well, also the terminal at the starter (be sure to properly jack and support the car while doing this), and the battery connections.

Good luck!

[bigchillcar]

i'd be curious to know the output reading with the rpm's more in the 2000+ range...could be weak diodes and simply not coming 'online' at the lower rpm value that it should, explaining the light at idle speeds, but not when driving, presumably above 2000 rpm's most of the time...preferably much, much higher...
ryan

[mudman]

Could it be that the battery is shot (less than 12v?, das not good if you've tried to charge it out of the car). I have had similar symptoms with batteries that turned out to be dead. Low voltage messes everything up!
-Jeremy

[targa80]

In the archives there are threads that provide information that is relivant to your situation. A similar problem of the alt light glowing very dim at idle and going out with increase in rpm. There are three exciter diodes in the alternator. The exciter diodes are not the power diodes that feed the battery and electrical systems. The exciter diodes supply feedback to the voltage regulator. the voltage regulator controls the the output of the alternator based on the exciter diode input. If the exciter diodes have deteriorated due to age and heat they will not function properly. I had this problem in my alternator. I ohmed out the diodes and they looked good. As I was probing the diodes one of the probes sliped and touched the body of one of the diodes. Well it just fell apart , I replaced all three with a generic 1N4000 diode and the low glow light problem went away. This is just my own personal experience and what I did to resolve the problem.

[vash]

Originally posted by mudman
Could it be that the battery is shot (less than 12v?, das not good if you've tried to charge it out of the car). I have had similar symptoms with batteries that turned out to be dead. Low voltage messes everything up!
-Jeremy

with my electrical skills, i learned along time ago to take the battery in to get it tested first thing. ok i learned this about a year ago when i spent too much money trying to fix my damn pickup truck and all it was? bad cell in the battery! but i could be wrong because it would still show 14+ volts at the battery with the car on, right? but you never can tell with electrical gremlins. besides it is free at pepboys.

[Ian Comerford]

I hope you don't mind me posting a thread that I have put elsewhere on the end of yours, just to see if anyone has any other ideas. The latest is as follows:

I have a similar problem on my 79 SC (UK spec). The alternator light and the brake warning light glow dimly when the engine is running at any speed. I have had the problem for 8 months and the car still starts and runs well. At 3000 rpm with the headlights on the voltage at the battery is 13.57, within the limits of 13.5 to 14.5. There is no fault with the brakes, indeed the warning light glows bright when you remove the cap from the fluid reservoir. I have 3 threads to follow; faulty alternator, faulty earth (ground), faulty alarm. Having checked out the charging side and the earth and only found one minor fault, I am now leaning toward the alarm's built in battery being faulty. However, I have now fully disconnected the alarm siren unit with its built in battery from the electrical circuit and.............no change!! Still got two dimly glowing warning lights on my dash.
Please keep the suggestions coming, we'll beat these gremlins somehow.
Thanks guys
Ian

[ischmitz]

You are not charging at all. The alternator light coming on when you turn the ignition to on says you have a good bulb. So far so good.

Now when it only flickers upon running the engine it sounds like D+ (the full alternator output that feeds the DF via the regulator) is not present. I would check for bad connections. Make sure whether you have an internal regulator or an external one. BTW: the rear windshield heater releay can easily be mistaken for an external regulator....

But hey, I am not an alternator specialist.

I once had a 2.7 where the ligth was constantly glowing. Putting a scope to the alternator output showed i had a funny pattern that suggested exactly one diode was open resulting in a somewhat noisy squarewave output. It would still charge the battery so I never bothererd to fix it.

Ingo

[Jamey]

Thanks for all the good info guys. I'm going to go ahead and pull the alternator out tonight and give it a look. If all connections appear to be good I'll take it over to the alt. shop and have them test/rebuild if needed. I took the alt. out and replaced it myself last time but, unfortunately, I can't remember if it had the internal regulator. I certainly could be mistaking something else for the VR on the driver side of engine compartment. I was thinking that the silver rectangular box with fins on it was the VR. It's bolted in between the 12 pin connector and the fuel filter and has a yellow sticker on it with lightening bolts. Also says BOSCH 12VOLT and VORSICHT on it. Anyway, I appreciate the tips and we'll see what the alternator looks like later this evening.


Jamey

[ischmitz]

That yellow sticker box is your CDI ignition box. The external regulator would be 1/3 of its size.

Ingo

[Lorenfb]

Internal regulator Porsche alt. have a allen slot in the shaft.

[Jamey]

Well it turns out I have a Valeo alternator with the VR attached to the back of it. The alternator shop said the alternator itself is fine but that the VR is out. Like Mr Cramer said, it was probably putting out just enough for there to be a balanced between alternator output and battery output. That would explain why my alternator light wouldn't light up with the engine running. Thats what was so confusing to me. Anyway, once again I appreciate everyones input.

Jamey