1987 Alt. not charging my 911

[lprowler]

Had a dead Battery about a week ago. Charged it over night and took the car to the auto parts store where bat. was purchased and had it checked. Bat. checked good, only have had the bat. just under 2.5 yrs., but the Alt. failed the check(not charging Bat.). Idiot light on dash comes on when key is turned on as it is supposed to, but after you start the car it goes out as if it is charging the Bat. which it is not.

Not being a trusting sole I went to a competing auto parts store, ask them to run the same check as first store and low and behold same results.

Ok, now I pulled Alt. out of the car (that was fun, I don't have small hands) and took it to an Alt./Starter rebuilding shop and guess what, they said that the Alt. tested GOOD. They cleaned it up, put some bearings in it and charged me a hundred bucks. They also taught me a little bit about how an Alt. works. According to them that small blue wire is the "exciter" which receives 12 volts to tell the Alt. to turn on and start charging the Bat.
Well mine was getting the 12+ volts from the Bat. but the blue wire(the "exciter") was only getting about 1 (one) volt.
After I went to start the car the idiot light came on and then I turned the key further and the car started and the idiot light stayed on, not charging. when I reeved the engine to over 3000 RPM the light flickered but stayed on?????
Any ideas, no fuses blown or anything like that.

Help

[Trakrat]

no name... no info on the car, last time this person/bot/AI posted, it was 4 years ago.
They have only posted 2 things since joining in 2009....????

And they have NEVER responded? I smell something fishy going on here....

[lprowler]

Hay Tack Rat,
no name no info on car.
the name is L.Prowler

the car is in the title of the thread "1987 Alt. not charging my 911".
I think your a Bot, certainly not an AI.

Lprowler

[30westrob]

The best check for charging is using a volt meter at the battery. Compare non running voltage to running voltage. Also running voltage with a charged battery should be at least 13.5 volts. I suspect you have an intermittent problem with your alternator.
Rob

[Noah930]

Once the battery is confirmed as fully charged up, take a multimeter to it as it's plugged into the car. At rest (car off) it should be about 12-13 volts, right? What happens when you try to start the car? What happens when the car idles? What about when the motor is revved to a few thousand rpm? What are the voltage readings with those actions?

[7783911]

check that you have the correct bulb in the gauge and its connected to the alternator ..thats what triggers the exciter on the alternator?

[Trakrat]

Originally Posted by lprowler

Hay Tack Rat,
no name no info on car.
the name is L.Prowler

the car is in the title of the thread "1987 Alt. not charging my 911".
I think your a Bot, certainly not an AI.

Lprowler

Ha! well there goes my theory...

[Hendog]

Originally Posted by Trakrat

Ha! well there goes my theory...

Yes, I’ve made a similar judgement call in the past
Trak, you have dug into your car far beyond what I have in the short ime you have ownwd it, more than I have in all my years of ownership. Well done!

[pampadori]

You might have a grounding issue. The ground strap near the transmission crossmember tends to develop too much resistance and can cause alt current not to make it to the battery.
This is really easy to test for though. Here is what you do....

Tools: Jumper cables, voltmeter.

Steps:
1. start car. Drive until warmed up well. (issue won't surface until warm from my experience)
2. Connect voltmeter to battery. what voltage are you getting while revving engine to 3k rpms? if its lower than say 13.7V then move on to next step
3. Take jumper cable (just one cable, can be the red or the black cable) and connect one end to the fan shroud or somewhere else metallic on the ENGINE. Connect other end to a ground point on the CHASSIS. There are a few spots under the decklid that would work. Hell, the decklid itself might work.
4. Rev to 3k again and check voltage again. Is it higher than it was in step 2? If so, replace the ground strap by the transmission crossmember under the car.

You're basically using a jumper cable as a temporary ground strap to supplement the likely very oily, corroded factory ground strap.

[SoCalSK8r]

I had all sorts of charging issues that nearly made me pull out the last remaining bits of my hair... turned out to be a poor ground connection at the battery. After that i went ahead and pulled all ground connections, cleaned em up as a precaution, and all is good.

I would also advise adding a volt meter somewhere. I use a simple on that plugs into he ciggy lighter and it works just fine.


Sent from my iPad using Tapatalk

[Jdub]

Good on you to find a place that would work on our older alternators - I think you did well to have them do what they did.

Now, when I had my Marchal rebuilt the light would also not go off - until I took the car out for a spin and the inherent resistance was overcome, causing the light to disappear. I learned after some work that every single darn ground (alt to engine > engine to body; Ground at battery - everything) needs to be scrubbed clean and coated. Also keep in mind that what appears to be a perfectly good braided or coated ground cable can be full of resistance via corrosion you can hardly see. It was most vivid to me years ago when my TR-6 would not start and I finally replaced the old battery ground cable with new. Curious, I opened the old cable up and the amount of molecular white powder within the cable told the tale.

Good luck!