Alternator Help

[jayhawk]

I am placing myself at the mercy of the court.

I have had a serious issue with the charging system the Pumpkin (1982 930)

A long story but here are the details:

Symptoms:

Battery not charging.
Tach acting crazy when battery losses power.

Facts:

1 - Battery fully charged (new) voltmeter on battery 12.7 V
2- While running battery voltage drops to about 11.7
3- Clearly battery is not being charged. Battery dead after a 1 day track event

Last fall, the battery was dead at the track after a few runs. Voltage while the engine running at the battery was 11.9

Obviously we thought alternator was at fault. Replaced the alternator with a Bosch rebuilt unit over the winter. After the first
t event this year, clearly the battery was not bing charged.

I took the alternator out this weekend and the local shop pronounced it to be working fine. I saw the 14.2 volts on the meter on the alternator test stand.

Here is what i have checked:

I have full battery voltage at red wire to the alternator.

I have 11.4 volts at the "blue" wire to the alternator when ignition is on at the alternator.

I have cleaned and redone all the grounds including replacing the engine to body strap and all the other ground points i could find.

I checked voltage at the starter connections, full battery voltage then a but lower while engine was running.

I connected en
gine ground directly to the negative battery post with no change in voltage results.

Clearly the alternator is not chargoing the battery. HELP

Bob

[Alan L]

Your diagnosis is a bit confusing.
Where are you measuring the blue wire V? That is your discharge light source.
Is that light on when running?
You have full V on the red wire when..? That wire is hooked in to the starter circuit so should read same as at starter.
Just an outside long shot - but a slipping belt would produce your symptoms.
Alan

[DaytonaCoupe66]

I expect that if you changed the alternator you confirmed that the ground wire from the alternator to the case was clean, fully seated, and not damaged. Mentioning it nonetheless as that is where my problem had resided.

[jayhawk]

Originally Posted by Alan L

Your diagnosis is a bit confusing.
Where are you measuring the blue wire V? That is your discharge light source.
Is that light on when running?
You have full V on the red wire when..? That wire is hooked in to the starter circuit so should read same as at starter.
Just an outside long shot - but a slipping belt would produce your symptoms.
Alan

Alan:

Blue wire measured out back at the alternator. Voltage when key is on, zero when key is off. Alternator light on with key on, off when engine starts.

I thought about the slipping belt, have checked it several times and it seems plenty tight and there is no noise etc that would indicate the belt is slipping. The old guy who checked the alternator thought that as well, he roughed up the belt surfaces on the pulley halves for me.

B

[jayhawk]

Originally Posted by DaytonaCoupe66

I expect that if you changed the alternator you confirmed that the ground wire from the alternator to the case was clean, fully seated, and not damaged. Mentioning it nonetheless as that is where my problem had resided.

I checked it for continuity but di not take it off and inspect closely. Might have to go back in and do that.

I am getting good at intercooler removal......

[908/930]

Possibly chasing the same problem, ordered a voltage reg to try and will let you know if I find anything else. I did find that somebody placed a couple of washers under the transmission ground strap where it contacts the body, I relocated those to under the nut side but have the alt out so have not re tried it yet.

[aschen]

zero expertise here, but It does remind me of the time I had a hard to chase charging issue caused by a diode in the dash. Have no idea if it is helpful but attached just in case:


I read 100+ Alternator threads

[jayhawk]

my car is a 82 gray market 930. I don't think i have the famous diode in the blue wire from the light in the gauge. The wore is only a few inches long then disappears in the factory plastic wiring harness cover. I assume the diode would not be back inside the cover of the harness would it?

[aschen]

not sure but mine is 84 grey market and did, cant remember how deep into the harness it was unfortunately.

[Alan L]

It is out of my depth, but the fact the charge light is not coming on must be a serious clue. To someone who knows this stuff. Which is not me.
Alan

[jayhawk]

Originally Posted by Alan L

It is out of my depth, but the fact the charge light is not coming on must be a serious clue. To someone who knows this stuff. Which is not me.
Alan

The charge light is on with key on and engine not running. After the engine starts, the light goes out, it is acting quite normally.

[908/930]

Mine was the same, looked normal. I just checked the + terminal on the starter was not real tight, so cleaned and retightened. Thinking about picking up a 50A/or100A battery tester and check the ground and + lead and connections under load with it.

[speednme1]

There is a diode under the dash that goes to the charge light. When it goes bad you will experience all sorts of charging issues that looks as if it’s a bad alternator but it is not. Top pic is the stock bottom pic is the one I made up. $50 vs $2

[jayhawk]

Originally Posted by speednme1

There is a diode under the dash that goes to the charge light. When it goes bad you will experience all sorts of charging issues that looks as if it’s a bad alternator but it is not. Top pic is the stock bottom pic is the one I made up. $50 vs $2

I appreciate the picture of the infamous diode, it has been hard to find one. I am fairly certain that my car (82 930) does not have the diode in the blue wire circuit. The blue wire connects to a spade connector on the bulb socket and disappears into the wiring harness. There is nothing attached to the wire. I will be home later today and confirm and post some pictures. At the alternator, I have 11.4 volts on the blue wire when the key is on and no voltage when key is off. Alt light in the gauge seems to be operating correctly, on with key on, goes out as soon as engine fires and runs. There is a funny connector thing (see attached picture for an example) back behind the gauge cluster but it is not connected to the alternator light circuit (will confirm tomorrow). I think it is in the wires for the gas gauge (does anyone know?)

Add info: about 10 years ago after the fan belt broke on track at RA we added an additional light to the alternator light, sistering it in to the spade connector on the bulb socket. Then this all started, I disconnected this light as it was an aberration although the car and charging stystem has been working fine for years and many track miles with the additional light connected.

I certainly appreciate all the assistance!! I cant help but think it has to be something relatively simple but having checked everything I have been told to check I am still lost. We can put a man on the moon and return him safely to earth but I cant figure out a "simple" 3 wire circuit. [

[Alan L]

Yes - this diode thing is a mystery. It has cropped up in a few threads before. I have an 82 930 - I will check mine today. But it does not show in my wiring diagrams.
Which makes it all a bit weird.
Alan

[Alan L]

OK - had a look under the dash and behind tach. Can't find anything that looks like a diode.
Alan

[jayhawk]

OK. PROGRESS!!

A closer look at the wiring revealed that theweird connector shown in the photos above was indeed in the alt light circuit, although in the red/black wire coming from the ignition switch not the blue wire going back out to the alternator. Looking carefully at it (I think when it was new it was clear and soft) there was clearly something in the middle of it connected in the red/black wire. Carefully prying the connector apart revealed the infamous diode!!!!!! It had the exact same part number 911-617-108-01 on it that was on the one I bought a few weeks ago from our host - $19. Also interesting is that the connector thing has a VW symbol on it!. So with care I salvaged the original wire ends from the connector and they looked too good to mess with. I connected up the new diode carefully and gave it a try.

At first, with the engine at idle the voltage did not drop below 12 as it had before and with my cousin holding the RPMs at a steady 2500 RPM the voltage at the battery slowly climbed and settled at 13.6!!!!

TA DA.

I let it sit overnight and I will give it a chance to repeat this AM before claiming victory.

Thank you everyone for your help!!!

B

[908/930]

Hopefully you found the problem. I cleaned all the terminals for ground straps put the alternator back in after checking the brushes ( the new voltage reg has not arrived yet) checked the diode in the dash appeared to work like it should, fired it up and 13.8v, must have been a bad connection.