HELP! Bad Alternator, or Regulator?

[freeride53]

Hey guys. Get in my car tonight and notice that my interior lights were dimmer than usual. Shrugged it off, and started driving home.

Once on the freeway, I notice that they are getting VERY dim, to the point that I can't read the OBC, and barely see the instrument gauges.

Then the ABS warning light comes on.
Then the warning light to the left of the fog-light light comes on.
Then the stereo starts flickering, then shuts off by itself.
Then my headlights start flickering.

Then 2 minutes later the warning lights go away, dash lights get bright, and the radio comes back on. 5 minutes later, it gets dimmer again, then I get home.

What's do you guys think is going on? Bad ground somewhere?
I don't think it's the alternator, because revving the engine doesn't effect the brightness/dimness.

Before all this happened, I drove through a puddle and had to park in a muddy lot. A friend tells me M20 cars have grounding wires below.
This car is a 91' 318i with an m42...is it the same on these cars?

Would appreciate all the help you guys have. Thanks!

Sina

[uturn]

Classic bad alternator leading to a drained battery.

[freeride53]

^ But for some reason, my car still starts! :(

[SlamedIAm]

I would start by getting your alternator/battery checked out because its free and relatively quick to do. The grounds in the engine bay are fairly easy to access as well you'll really only need to remove the AFM. There is a good chance the lower ground by the oil pain ias heavily corroded/losing its insulation. Mine was pretty gnarly so I replaced it with one from Gregs///M.

If yours isn't in too bad of shape you can at least clean it up while you're there.

[ST1G]

I had a similar issue and it was the brushes inside the alternator. Cheaper than a new one.

[Old city bimmer]

definitely sounds like your alternator.

[AndrewBird]

The car will still start and run with a bad alternator. The engine just runs off the battery and slowly drains it. Your battery light should have come on though.

I'd check the engine ground strap that goes from the oil pan to the frame rail on the driver side. Also check/clean your battery terminals and make sure the ground is attached to the body well.

There is also a terminal block on the passenger side of the engine bay. Check/clean everything there as well.

Lastly, check the battery voltage. Should be ~12.5v with the engine off and ~14v with the engine running. If it doesn't read 14v when running, your alternator is likely dead.

[E30NJ]

Ever figure it out? I'd like to know. :)

[freeride53]

Update!

Decided to drive the car to campus tonight and on my way, everything started going dim.
Headlights and foglights stopped working completely, interior went black.

As I parked the car was struggling to hold an idle and roll the windows up.

Turned it off, and now it wont start again.

Could this be the regulator? Could I replace it without removing the whole unit?

It's gonna be my first alternator or regulator job! During finals week :(

[dnguyen1963]

Your alternator/voltage regulator is dead and not charging your battery. Check the regulator first because it can be removed with little hassle. Have you charged your battery and check to see if it holds charge?

[freeride53]

^ Can the regulator be removed without removing the whole alternator unit?
And what could be signs/ways to check that piece individually?

Also - no means of charging the battery myself...student living on campus and all my tools are 600 miles away :(

[reelizmpro]

Yes you can change the regulator without removing the alternator. At least you can on an M20, not sure on the M42. Just remember to disconnect the battery first. Brushes are probably worn below spec. Specs are in the Bentley manual but if you never changed it...chances are it's due. Mine lasted 200K before wearing down.

[freeride53]

^ Good to know. gonna remove the airbox and see how much room I have to play with.

Barry, when your failed, did you experience similar symptoms?

[freeride53]

Here's an update.

Me and a friend tried bump starting the car, it didn't work.
Found a neighbor with cables, he jumped my car right to life.

Let the car idle for 15+ minutes. Shut it off, won't start again.

Now trying to get my hand on a voltmeter to see if the battery will read 13.5 V

[estoguy]

I'd be checking the regulator first.

Same thing happened with my car a few months ago. The regulator was badly worn. But it also went just shy of 200K miles before crapping out.