Voltage drop during hard stop

[andrewwynn]

Originally Posted by bugbyte

on, the voltage bouncing around in the upper 12 v and lower 13 v and fail on the voltage regulator test.



I need and suggestions before I replace the alternator as it is water cool.

Not sure how I missed this but the alternator should hold Rick steady voltage any load and any speed. The biggest instant load you can apply is probably the rear defrost with seat heaters.

If you are able to get sub 13v at idle not moving measure the vDrop from engine to chassis and see if you can measure any voltage drop on the ground.

Then using OBD measure the vBat and see if you can get it to hiccup with a throttle off with heavy load (wipers and defrost/seat should do it) if you can get a voltage drop of more than 0.4-0.5v from that test the voltage regulator is not doing its job.

I've recently removed and replaced an alternator on an M62 very similar it was way easier than the air cooled one on my M54 other than the annoyance of course of having to drain the coolant. Either case have to remove the fan.

I've never taken apart the water cooled models to figure out what it takes to replace the brushes and slip rings but it saved me almost $300 to refurbish mine vs replace it