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      07-03-2019, 06:39 PM   #10
MrSweet1991
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Drives: BMW E90 330D M Sport
Join Date: Apr 2017
Location: West Midlands

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Quote:
Originally Posted by N5GKP View Post
So, if you can access the instrument cluster secret menu set it to the voltage screen.
Go for another drive and watch the voltage, when you accelerate does the voltage sporadically drop to around 12.3-12.6V? And then brake and see if it returns to 14V+,
If thats whats happening id be happy to say I don't see it as an issue. 'Smart' alternators tend to switch on and off quite often when driving, for efficiency's sake BMW have tried to work it so when the engine is under load, unless necessary the alternator will briefly turn off and then turn back on when on overrun / deceleration.
Right, so just to update on this I "think" I've fixed the issue! So, knowing I have a good battery and I know the alternator (when it does output 14v) runs very well and doesn't fluctuate with things like AC, Lights etc we have to start thinking in between so my theory was, if it was a ground strap then from what I'm aware the car would probably randomly stall, or a bad ground strap can result in slower cranks where mine is pretty strong. So, I thought the voltage regulator may be somewhere to start, having done some research the voltage regulator is a common part to fail, then I found out the reason they fail is usually due to the brushes wearing out. This in itself was good to know because, assuming these brushes where on the very peak of just about touching the slip rings then maybe that's why sometimes it works and sometimes it doesn't

So, I purchased a Valeo alternator replacement brushes set (more specifically sv72) I took my alternator off and i could see that the inner slip rings where quite black, an indication that the brushes aren't making good contact, the top brush also was shorter. So I replaced the brushes and started the car and I got 12v but realised I had forgot to put the black connector into the alternator which actually connects to the voltage regulator and it rose to 14v so that in itself was interesting, if that plug isnt connected it wont output 14v, and of course if that connector connects to the voltage regulator and that is powered by brushes then if those aren't working good that would explain why it wouldn't always output 14v. Ibe started to car around 5 times now but tomorrow will be good, but man for a few hours work it cost £2.70!
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