Voltage Regulator? Alternator?

[the_e92]

I've had this recurring issue with my 2008 M3 that has been causing me nothing but trouble. It started a few months back when the car wouldn't start on a cold morning, thought okay must be a battery issue. Went out and replaced the battery and worked well for about a week then another no start, thought thats odd, new battery registered the whole nine yards. Then I started watching my voltage as I drove, 12v. ah must be the alternator, head over to my local shop to get it tested, they can find nothing wrong with it, running at 14-15v now just fine, weird maybe an anomaly. Nope, it seems to vary every time I turn the car on, sometimes 12 volts, sometimes the full 14 and sometimes as low as 9. My solution the past few months has been turn the car off and back on until it says its charging at 14 volts then the car will be good until turned off again (I've driven 400 miles and it never went below 14, as long as it started at 14 it would stay but if it started at 12 or 9 it would stay at those numbers and the battery would die slowly as I drove). Now with my limited knowledge, it sounds like the voltage isn't being regulated properly so I should just change the voltage regulator and everything should work fine right? Or should I bite the bullet and replace the whole alternator at this point? Anyone dealt with this issue and know the solution? Car throws no codes besides battery discharge. Thank you.

[pbonsalb]

Ground cable under the car? IBS cable at the battery? Main power cable recall (under passenger dash?)never done? Alternator voltage regulator?

[the_e92]

Originally Posted by pbonsalb

Ground cable under the car? IBS cable at the battery? Main power cable recall (under passenger dash?)never done? Alternator voltage regulator?

Could be any of those but with it changing so quickly just after turning the car off then on again I don't think it would be a physical connection that's going wrong because if it was a physical connection, it would go wrong and stay wrong right?

[Redd]

Ground cable is easy to check and cheap to fix, so check that first. IBS rarely fails. Main power cable normally results in the car being difficult to start, so I don't think its that.

If your alt is over 80k kms it's already on the death clock. Just a matter of time before it leaves u stranded. Now whether it's the whole alt or just the voltage regulator, that's 50/50. You can gamble and just replace the voltage regulator, some have had success some not. If it were me, I'd just replace the alt and not worry about it anymore. I've been stranded by a dead alt in the middle of morning rush hour and don't want to go thru that again.

[pbonsalb]

My 2008 had intermittent no starts when it got cold one year and the culprit was the factory ground cable, but there could be other reasons why normal battery starting power is not available.

When the car does not start, put a multimeter on the battery to check the voltage. If below 12, there is either an improper draw when the car is off or the battery was not charging when the car was running.

Using a jumper cable just as a ground from block to chassis, assuming good contact points, with show whether the factory ground cable that disintegrates by 10 years on cars driven in rain and snow is the problem.

I disagree that an alternator with over 80k km or 50k miles should be replaced. They last much longer than that. But a worn voltage regulator is a possibility.

For the IBS cable, just bypass it temporarily as a test.

[the_e92]

Originally Posted by pbonsalb

My 2008 had intermittent no starts when it got cold one year and the culprit was the factory ground cable, but there could be other reasons why normal battery starting power is not available.

When the car does not start, put a multimeter on the battery to check the voltage. If below 12, there is either an improper draw when the car is off or the battery was not charging when the car was running.

Using a jumper cable just as a ground from block to chassis, assuming good contact points, with show whether the factory ground cable that disintegrates by 10 years on cars driven in rain and snow is the problem.

I disagree that an alternator with over 80k km or 50k miles should be replaced. They last much longer than that. But a worn voltage regulator is a possibility.

For the IBS cable, just bypass it temporarily as a test.

Sounds like it's just a good idea to replace the ground cable especially after having driven in plenty of snow here in idaho. Probably be buying a new ground strap, not sure if it's ever been replaced on a 177k mile car, and alternator to try and get to the bottom of the random drops in charge. The voltage regulator is just on the back of the alternator and when I buy one it should come with one correct?

[pbonsalb]

Yes, replacement alternator has voltage regulator. Give that ground strap a tug. At 177k miles you might be holding it in your hand. Mine came apart at about half that mileage.

[Helmsman]

OP, bumped into this one talking about a lose nut on the alternator, might be worth checking out: https://www.m3post.com/forums/showthread.php?t=1444544

[the_e92]

Originally Posted by Helmsman

OP, bumped into this one talking about a lose nut on the alternator, might be worth checking out: https://www.m3post.com/forums/showthread.php?t=1444544

After reading through that, when I recently replaced the battery I remember there being a little bit of rust in the battery well, so I'm going to take the battery out, check the connection in the bottom of the well and make sure it's not too corroded to the point of losing voltage between battery and alternator.