Revs on 540i N62 V8 rising and dropping

[Chrisblob 3]

Hi all, I've noticed in the last few months what seemed like a tiny issue that suddenly got a lot worse last night. A few months ago I noticed that the engine while idling or while holding a fairly slow speed, particularly while still warming up, the revs would rise very slightly for a few seconds, then drop back again for a seconds then repeat until the car was at normal operating temperature when the issue seemed to go away - it would only rise a small amount say from 1200 to 1220 rpm, just enough to notice a pitch change in the sound of the engine. However last night while driving home after a 4k trip to grab groceries, I noticed that the revving issue was now affecting the car at full temperature, and the difference in revs was much greater, roughly 1200 rpm to 1400 or 1500 rpm - by the time I got home I noticed that the headlight and tail light brightness would rise and fall with the engine revs. I turned the car off and let it sit for a couple of hours, then turned it on and let the engine idle, which it did without any rise and fall in revs - I'll take it for a drive around the neighbourhood tonight and see if the rise/fall thing starts happening again. Has anyone experienced a fault such as that before? I wondered if the alternator or some electrical system was malfunctioning but the battery is quite new and still has plenty of kick to turn over the N62.

TIA for any helpful hints and advice,

Chris W, Chch

[Chrisblob 3]

I think I've identified it - after a test drive the car didn't seem to be misbehaving much, but as I finished the test drive iDrive spat out a warning to say there was a charging fault. I checked the battery and it was down around 11V, so it isn't getting a proper charge from the alternator. I'll get the alternator out and check if the copper contacts on the rotor are OK, and if they're good hopefully a fresh set of bushes will sort it out for me

Edited August 8, 2023 by Chrisblob

[Chrisblob 3]

On 8/8/2023 at 9:39 PM, Chrisblob said:

I think I've identified it - after a test drive the car didn't seem to be misbehaving much, but as I finished the test drive iDrive spat out a warning to say there was a charging fault. I checked the battery and it was down around 11V, so it isn't getting a proper charge from the alternator. I'll get the alternator out and check if the copper contacts on the rotor are OK, and if they're good hopefully a fresh set of bushes will sort it out for me

...which leads me to my next question: does anyone who has owned a BMW with the N62 or N62TU know of a reputable supplier who can provide a reasonably priced 12V 180A alternator for that engine, or perhaps even a refurbished alternator? Options in Christchurch seem extremely limited or extremely expensive, so I'm prepared to look nationwide or even overseas to source a replacement if the one in the car currently cant be refurbished by myself with new bushes

Cheers,

Chris W, Christchurch

[Palazzo 477]

Seem to be under $500 delivered from overseas.

[arktis 58]

Part# looks to be 12317542934.

Few options I can think of:

Search "BMW E60 wrecking" on TradeMe. (Just found at least 2)
Try Brent/BMWorld.
AllEuroParts for a new/refurb.

[aja540i 1906]

Could be the regulator which can be replaced separately, it has the brushes attached so 2 birds with one stone. I did the one on the M5 its a PITA to get at but way cheaper than a whole alternator.

[Chrisblob 3]

On 8/11/2023 at 4:01 PM, aja540i said:

Could be the regulator which can be replaced separately, it has the brushes attached so 2 birds with one stone. I did the one on the M5 its a PITA to get at but way cheaper than a whole alternator.

Cheers, I've removed the air intake gear and the oil cooler/fan unit so I could reach down the front of the block. I got the serpentine belt off, but then came to a complete stop because it appears the N62B40TU V8 engine in my 540i has a %#$@&* water-cooled alternator - apparently in some N62 powered vehicles there is a lack of airflow around the alternator, so they use water cooling to prevent overheating. So to remove the alternator I would have to drain the coolant, do what needs to be done with the alternator, then refill the coolant and bleed the cooling system. I just don't have the gear or space in my tiny single garage (or patience) to do all of this, so I'm going to have to put it all back together and get the car to a local mechanic, and hope he is able to do the work required without it costing an arm and a leg - disappointing to say the least. It's as if car makers design modern vehicles specifically to be difficult to work on. Never mind 🤔🤦‍♂️