1984 318i won't charge at idle?

[Graebmw95]

Hey guys, so a couple months ago I had an issue where I;d be driving the car and it would just die... What ended up happing is that he ground on the alternator had snapped so it burned itself out. So I replaced the alternator and well... nothing. So i did a little more research and found I need to changed the bulb in the cluster, even though the bulb never turns on? Even after putting a new bulb in?

Anyway, that fixed the problem for the most part except....the alternator doesn't charge the battery below 3500 rpm. I kind of just shrugged it off and figured it was a weird design. It didn;t effect me and my car still ran great...

Until... today. It snowed for the first time this season and its been 10 degrees for the past two days. I went out this morning to start the car to warm it up before heading to work. When I turned the key it cranked really slow but still turned on. I come back out about 20 minutes later and the car is dead.. So i jumped it and as soon as i took the cables off it died... SO

The question is why won't the alternator charge the car below 3500rpm? I also haver a new battery.

A couple of things I'm going to check, the light bulb and the alternator ground cable and make sure its grounded to a good ground.

Any ideas? ):

So I went ahead and took the alternator off and looked at the VR.. I don't know if this is okay or not maybe you guys can shed some light on if i need to replace it?
Also, one of the blue wires isn't connected and the other is loose, I'm assuming thats the exciting wire correct?
(adding pics in 1 minute)

[bmwguy325is]

Did you buy a shit part? As in what brand? Was it new or reman?

[Graebmw95]

Did you buy a shit part? As in what brand? Was it new or reman?

Pretty sure it was a good part, it was under warranty and I got it replaced. It's Bosche.

[Graebmw95]

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[Graebmw95]

Bump


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[2mAn]

Any ideas? ):

So I went ahead and took the alternator off and looked at the VR.. I don't know if this is okay or not maybe you guys can shed some light on if i need to replace it?
Also, one of the blue wires isn't connected and the other is loose, I'm assuming thats the exciting wire correct?
(adding pics in 1 minute)

sounds exactly like the problem I had with my old Rabbit. The exciter circuit wasnt complete until I added the light so it never charged the car. This was fixed once you changed the bulb, but for whatever reason it wouldnt start charging the car until it had cleared 3500rpms once, so Id say get the system charged and make sure on every drive you rev it once past 3500rpms. On my rabbit the light wouldnt turn off until I had done that once, Im sure with the archaic system the M10 runs off of, its the same issue.

TLDR: Weird problem, simple solution = r3v it past 3500rpms once on every drive to make sure the alternator charges the battery.

[Graebmw95]

sounds exactly like the problem I had with my old Rabbit. The exciter circuit wasnt complete until I added the light so it never charged the car. This was fixed once you changed the bulb, but for whatever reason it wouldnt start charging the car until it had cleared 3500rpms once, so Id say get the system charged and make sure on every drive you rev it once past 3500rpms. On my rabbit the light wouldnt turn off until I had done that once, Im sure with the archaic system the M10 runs off of, its the same issue.

TLDR: Weird problem, simple solution = r3v it past 3500rpms once on every drive to make sure the alternator charges the battery.

Well the problem is even once i've cleared 3500 rpm it still wont charge lower than that. I fixed the blue wires and i though it fixed it, but this morning i went to warm the car up and when i got back it was dead, even though it idled just fine the other day?


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[dnguyen1963]

What is the voltage output from your regulator? Did you check?

[kway]

So you're saying you need to hold the r3vs at 3500 or higher to keep it charging?

[Jaxx_]

So you're saying you need to hold the r3vs at 3500 or higher to keep it charging?

no. fix the exciter circuit or rev it to like 3500 and the alternator will kick on. You can keep it under 3500 after that if you'd like.

[Graebmw95]

But the issue is it doesn't stay on. It only charged above 3500 then if i let it sit for too long below it will die.


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[Jaxx_]

But the issue is it doesn't stay on. It only charged above 3500 then if i let it sit for too long below it will die.

Okay.

What is your voltage at idle?

What is your voltage at 3500?

Does the battery light come on with the motor off and the ignition on?

Does the battery light go out with the motor on?

Have you inspected your grounds and battery cables and their respective connections?


charging issues are fairly easy to sort out, but you need to do some ground work.

[jeffnhiscars]

It sounds like a VR issue and that solde doesn't look very well done so I'm wondering if someone messed with it. Either way that would be my guess