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Discussion Starter #1
Hello,
It's sad but true that I am from Austria, neighbour of Germany where our cars where produced and need to get help in an english forum :)
Actually, i have 2 problems that make me grey hairs already, and I am not sure if there is a Connection between them because the first came long before the second

The first one is that, especially after cold start, the engine changes the exhaust sound (not basically the rpm) in very hearable steps (jumps), it feels like something is regulating, but not smooth and it was not before.

When I drive berween 1500 and 2000 rpm, I can hear this also even when the engine is hot. Most people wouldnt hear it, but it was not before, so I think something is not ok.

The second problem is thet the car goes sometimes in limp mode ("engine power reduced,...")
When it is in limb mode, the sound jumps are not anymore.

When it goes in limb mode, ist ALWAYS in P500 mode + full throttle and more then 7.000 rpm. Its courious that the problem is ALWAyS: idle contriol unit; SMG CAN BUS OFF (CD8B)

It doesnt make sense because the idle Control Units are not used at full power and there are 2, but no specification which one it is

I checked and cleaned the throttle acturators already, but they seem to be ok , and I checked the wiring of the idle Control Units,

Can it be that one of them is defective and makes that unusual symptom?
And what can be the reason of the Sound jumps?

Thanks for your help in Advance
 

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Not sure on the limp mode, but for the idle undulation, my e63 M6 has always done this and had gotten worse and worse over the past years...only during the warm up cycle and then very faintly on warm restart (like starting back up after going into a store for a few minutes).

But, After doing my rod bearings and vanos line replacement recently it has almost totally gone away on the warm up cycle...made me nervous because it has never sounded this good on startup until now, lol. I know it had nothing to do with the actual rod bearings or vanos line change, but suspect it was either the bleed process for the vanos that is required when changing the vanos line, or possibly a bad vacuum connector on the plenum as I found a broken connector that may have been allowing air in. The connector was one of the two small ones between the plenums and the firewall...looked like someone before me didn’t know it was back there and tried to remove the plenum without disconnecting it.

I actually made a video series on doing the rod bearing job...you can see the vacuum line connector in the part 3 of 13 video on removing the plenums that was broken...below is a link for reference. The broken connector that was on mine is shown at the 11:20 time mark on the video.


Not sure which might have gotten rid of the strange cold start undulation, but the two items seem to make the most sense on things that could affect it. I guess any of the vacuum connectors could cause this too if that was the reason it was doing it (vacuum leak). If it was the vanos system that had some air trapped in it over the years, the vanos bleed would be what took care of it.
 

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Discussion Starter #4
Thanks a lot for the competent information. Is there a possibility to check for leaking vanos pipes except opening everything, so that they can be changed with same efforts? I have this annoying vanos sound that started with 30 tkm already, only when the oil is hot and around idle rpm:
Can it be occured by leaking vanos pipes?
 

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Sounds almost like there is air trapped in the Vanos unit. Mine did the same ironically also on bank 2 (my car had been sat for a few weeks though), the garage ran a Vanos bleed routine at my request and the noise has not returned since.
 

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Discussion Starter #7
Thats a good idea... so the air can be trapped and can't go out without bleeding???
 

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Yep, there's an ISTA routine to bleed both the Vanos units - its a good idea to run it a couple of times when you do it
 

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When you guys had this around the Rev range you mention 1500-2000 when the pitch changes do you get a slight surging when driving (like slightly more power slightly less power all the time in the range especially when cold)
 

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Discussion Starter #10
@pyro225 yes, ist exactly this behavior you described, feels like slightly pulsating power (and exhaust sound) at constant throttle… but where dors it come from?
 

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Ok this has been driving me nuts - I have a tubi exhaust so hadn’t heard much from up front but defo noticed this - have you tried the bleeding yet?
 

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Discussion Starter #13
I need the bmw servive center to do the vanos bleeding, correct?
I just have the problem that the secundary pump doesnt start at cold engine, but this comes from the ECU, the hardware is ok. If I ground the responsible pin of the ECU, the pump starts...
Also a bit courious....
 
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