Failing Battery or Alternator???

[Sea Aych]

So I'm in Vancouver BC, really far from home and some funky stuff has started to happen.

Background:
M50nv swapped 325i
Speedo and mpg gauge haven't worked in a while (on throttle, mpg gauge is pegged to the right, off throttle it's pegged to the left. Broken)

Problem:
Two days ago at highway speed, the car just started cutting out, losing engine and electrical power (turn signals not even working), then coming back to life, and cutting back out again, over and over until I slowed down below 80kph/50mph. I could tell it was about to bog because the mpg gauge would become unpegged from the right and float around randomly.
Then I pulled over and stopped, and it wouldn't start again. Battery voltage 12.04V. Weird.
I got a boost and it drove fine below 80kph/50mph, and would start again no problem.

Today, same exact problem, but I noticed my battery voltage when the car is off is 15V, and when running just above 16V. It hasn't bogged yet, but the mpg gauge still floats around at higher speeds, and I'm getting a faint (way more faint than the rest of the dash lights like parking brake) flickering of the battery light.

Any ideas? I'd like to get this sorted before any more long drives to get home.

The battery is a few years old too but hasn't given me problems in the past 11000km in a month and a half.

Thanks!

[george graves]

16volts is way too high - I'll guess it's a failing voltage regulator. Replace it ASAP.

[Sea Aych]

16volts is way too high - I'll guess it's a failing voltage regulator. Replace it ASAP.

Any way I can test it? I've got a multimeter and all my tools with me

[jlevie]

You can test the alternator while it is still in car. See the Alternator Diagnostics my parked thread at the top of the forum.

But the battery voltage you've measured is way out of line. Try a different, higher quality, DMM.

[george graves]

Any way I can test it? I've got a multimeter and all my tools with me

If you're actually getting 16 volts - then you just did test it.

That's why the voltmeters I sell, I make sure they read up to something like 16 volts -accurately-. It's bad times when your voltage regulator fails in such a way that it over-volts. That's - umm "bad". In some cars it will just blow out a few bulbs, others it can start to mess up things like fuel pumps and blower motors, ect. The ecu has some good protection to it, but I could see a situation when an overvoltage could cause it to shut down. But honestly - that's just an educated guess.

But the battery voltage you've measured is way out of line. Try a different, higher quality, DMM.

Even the $3 harbor fright's DMM's aren't *that* far off. Most is 1 volts off on those cheap-o meters. But it could be a bad meter. I guess????

But it's not uncommon for v-regs to go high when they are going bad, and when they do, it's a bad situation. It can cause all sort of damage/problems.

[Sea Aych]

Guys I think I found the problem. Here's the VR

[Sea Aych]

For the record I discovered the left one isn't actually worn down as far as it looks, it's just stuck compressed into the housing like that. Seems like at higher speeds it could lose contact or something

[jlevie]

That is not right... Replace the VR with a BMW OE or OEM part.

[Sea Aych]

That is not right... Replace the VR with a BMW OE or OEM part.

If you're actually getting 16 volts - then you just did test it.

That's why the voltmeters I sell, I make sure they read up to something like 16 volts -accurately-. It's bad times when your voltage regulator fails in such -snip-

New VR fixed it. All done in an hour.
Thanks for the quick help narrowing it down guys!