Backfiring then dies

[jonmon6691]

So this morning my car needed a jump start to get running and I put the battery on a charger when I got home. It started up just fine a few hours later, but then started stumbling and loosing power over the course of 20 minutes, the headlights, dashlights, and taillights got progressively dimmer and I had to keep my foot on the gas and the rpm's at 3-4k at stop lights to keep it from dying, which it eventually did. I had AAA tow it home.

I'm guessing it's the alternator or battery at this point, but I'm not sure. Does what I described sound familiar to anyone?

[jlevie]

I'd guess, based on what you've said, that the alternator isn't working. But in that case you should have had the BATTERY light on. Does that light come on when you turn the key to ignition on before starting the engine? I don't know what car you have, but for most of the E30 production that light is a critical part of the charging system and if the bulb is burned out the alternator won't charge.

[jonmon6691]

Well I have a '87 325e. And the battery light doesn't come on when I turn the key to "on" other lights on the dash do turn on so its not completely out of charge. Should I try replacing that light first?

[lennon]

listen to jlevie. it sounds like that battery light bulb is burned out. so, yes replace it.

[jonmon6691]

I replaced the light and tightened the alternator belt. The battery light still does not turn on when I put the key into the "on" position and there are no blown fuses in the fuse box under the hood. I jump started the car it it had the same symptoms as before, rough idle then stalls when I use power (turn on high beams)

[jlevie]

To diagnose this, remove the exciter wire (the smaller of the two) from the alternator, ground it, and turn on the ignition. If the bulb still fails to light there is a problem in the cluster, wiring, or in C101. If the bulb does light, replace the voltage regulator in the alternator, or the alternator.

[jonmon6691]

So grounding causes the battery light (and brake fluid light) to turn on. I'll go to napa and see if they have the regulator.

edit: So the brushes where very very short. I'll replace it tomorrow morning, I'm hoping that will clear this up.