Car doesn't stay charged/dies quickly + parasitic draw

[Andy348]

Drove the car last month, it died within about an hour of driving. Figured it could be the alternator, but the battery was old so I bought a new battery and put that it. Car ran great, parked it for the night, and it was dead the next morning.

So I've got a used, working alternator on the way that I'll put in whenever it arrives. However, I searched (albeit after purchasing the alternator) and read about the light in the cluster that sends a signal to the alternator to start charging. I couldn't get much more information than that though.

I'm going to put in the alternator and see if that fixes it, but if not, what can I look at next? Grounds looked good, but the main ground seems a bit suspect.

Also, the car has parasitic draw. I hooked up the test light and pulled the fuses one by one, but no fuse made the light go out. What's my next step?

Thanks

[jlevie]

A test light may not tell what you need to know. There are parts of car that normally draw current (30-60ma) from the battery. The only way to check for excessive parasitic draw is with with an ammeter placed between the battery negative terminal and ground.

The battery/alternator warning light in the cluster is the source of exciter power for the alternator, without exciter power the alternator won't work. If the light doesn't come on when the ignition is switched on, the bulb could burned out, one of the cluster fuses could be blown, there could be a wiring fault between the cluster and alternator, the engien to chassis ground strap could be bad, or the exciter winding in the alternator could be open.

[Andy348]

What would be considered excessive draw?

Are the cluster fuses in the fuse box?

Exciter winding in the alternator open = would be fixed by a new alternator?

Lastly, on a slightly unrelated note, the tachometer doesn't move at idle. It works fine while driving, but at idle it reads 0. Related or unrelated?

Thanks Jim.

[jlevie]

What would be considered excessive draw?

Anything above 60ma.

Are the cluster fuses in the fuse box?

Yes.

Exciter winding in the alternator open = would be fixed by a new alternator?

Yes. But check everything else before replacing the alternator.

Lastly, on a slightly unrelated note, the tachometer doesn't move at idle. It works fine while driving, but at idle it reads 0. Related or unrelated

I'd suspect a bad SI board or even a bad tachometer.

[ONRAILSM3]

What is your charge voltage? Engine running, across the battery? If it's lower than 13.6 you need an alt. Shut it off. What is the voltage? Less than 12 you have a dead cell.

Many Bosch alternators have a replaceable voltage regulator. It's a plastic thing that bolts to the back of the alt with two screws. You do not always have to replace the whole alt if the armature is good.

Read this, it's how to correctly test for draw.

http://www.popularmechanics.com/cars/how-to/repair/how-to-stop-car-battery-drains

[Andy348]

Okay, I ordered an alternator but it was lost in shipping. I've got new lights for the cluster coming in this weekend.

I can't check the charge voltage until Saturday, but I will do so after I put in the new LED and reinstall the cluster. Could of questions:

1) If the battery light on the cluster is the reason it isn't charging, will removing the cluster temporarily fix the problem?

2) If I replace the light bulb and the light comes on, do I assume that it is fixed? I assume I will confirm by checking the charge voltage across the battery as OnrailsM3 mentioned.

3) I've got an E alternator on the I engine. If the alternator is the problem, is it fine to have the E one rebuilt, or should I go for the I alt?

Thanks
Andy

[jlevie]

Okay, I ordered an alternator but it was lost in shipping. I've got new lights for the cluster coming in this weekend.

I can't check the charge voltage until Saturday, but I will do so after I put in the new LED and reinstall the cluster. Could of questions:

1) If the battery light on the cluster is the reason it isn't charging, will removing the cluster temporarily fix the problem?

No. The current flow through that bulb is the exciter current for the alternator. If the bulb is bad or the cluster is removed exciter power doesn't reach the alternator.

2) If I replace the light bulb and the light comes on, do I assume that it is fixed? I assume I will confirm by checking the charge voltage across the battery as OnrailsM3 mentioned.

If the alternator is good, replacing the bulb may be the fix. But worn brushes, a bad voltage regulator, or a bad alternator are possibilities.

3) I've got an E alternator on the I engine. If the alternator is the problem, is it fine to have the E one rebuilt, or should I go for the I alt

The E alternator is fine.

[reelizmpro]

Sounds like the alternator or voltage regulator (inspect brushes first) since it died while running. 84-85 year models had that problem with the cluster light. If the bulb was bad, it wouldn't charge so sometime in mid 85 BMW put a resistor in parallel with the bulb so if the bulb goes bad, the alternator will still charge. If you have an 86 on up cluster* then you don't have to worry about this.

That's some drain you have. Check the trunk light bulb. Put your cell phone on video capture mode and place it in the trunk then close. Then check the video to see if the light turned off. If it didn't turn off, you may have to adjust the trunk latch tighter until it does. They tend to get loose and cause the switch to not make contact. It's tough to figure out because it's the trunk light. It happened to me once, always check the obvious before pulling your hair out looking at ETM's and chasing ghosts.

[Andy348]

Thanks for all the help guys.

Finally got my hands on the car today. I switched the cluster battery bulb for a working one with no difference. I then beefed up the main ground to the chassis via jumper cables, and then grounded the stud on the back of the alternator to a valve cover nut. Nothing changed.

At 1500rpm, my charge voltage is 12.4-12.5 volts. According to the Bentley, this means I need a new/rebuilt alternator.

The parasitic draw seems to have fixed itself with the removal of the deck faceplate, so I shall take a look at the stereo wiring when I have more time.

I pulled the alternator and I'm getting it rebuilt later this week.