Alternator not charging at idle

[doctorx]

I searched and failed for this particular issue. At idle and particularly when starting up, the alternator doesnt charge. The abs and bat light comes on. I measured and it was at battery voltage (12.8?) If i blip the throttle, the lights go out and i test 14.3v. The thing is it isnt consistent. I have another issue which i think may be related, If I do a hard pull in 2nd gear, the engine will cut for a second and then catch. I noticed when it is doing it the rpm gauge acts like it is shut off during the same time. When the engine catches, the dash is back to normal. I am planning on changing the engine ground strap this weekend. Also when running off battery the engine smooths out (i am not sure what this even means).

What could be causing it?

If there is a post that addreses this, please send it my way since i apparently failed that part.

[MrBurgundy]

The cutting out and gauge failure (i'm assuming tach) may be the CPS going bad.

The charging at idle could be a faulty regulator. Cheap and easy to replace both.

I'm not sure what you mean by runs smooth off the battery

[reelizmpro]

What's the year and model of your car?

[doctorx]

1987 bmw 325i convertible. CPS? Crank position sensor?

[McGyver]

[INDENT]I searched and failed for this particular issue. At idle and particularly when starting up, the alternator doesnt charge. The abs and bat light comes on. I measured and it was at battery voltage (12.8?) If i blip the throttle, the lights go out and i test 14.3v.

My car does the same thing on every startup. I just blip the throttle and go about my day. Its probably something in the cluster not exciting the alternator correctly.

[reelizmpro]

On 325's you shouldn't have to rev the engine to excite the alternator. It should start charging right after startup.

[doctorx]

I tested d+ and b+ and just got 10.7v coming out of the new alternator from b+. I took it out and too the old and new one to orielly and they both tested good. Confused i went back home. I decided to swap the diode and put the old one back in. And it works great. The bat light comes on before start and goes out after start. abs light didnt come back on.

So i think 4 possibilities:
1. I replaced the engine ground strap. I was going to do that while i was in there anyways. The old ground strap didnt look bad.
2. the diode was bad (but tested fine at oriellys)
3. Loose wire, but didnt notice any when i took alternator out.
4. luck.

So it is fixed, but not exactly know which one fixed it. I think i can an alternator swap in my sleep now though.

[McGyver]

I tested d+ and b+ and just got 10.7v coming out of the new alternator from b+. I took it out and too the old and new one to orielly and they both tested good. Confused i went back home. I decided to swap the diode and put the old one back in. And it works great. The bat light comes on before start and goes out after start. abs light didnt come back on.

So i think 4 possibilities:
1. I replaced the engine ground strap. I was going to do that while i was in there anyways. The old ground strap didnt look bad.
2. the diode was bad (but tested fine at oriellys)
3. Loose wire, but didnt notice any when i took alternator out.
4. luck.

So it is fixed, but not exactly know which one fixed it. I think i can an alternator swap in my sleep now though.

Those are the best fixes. "I don't know why it's working, but it is!"