E71 2009 N54B39 - problem with rough rpm when accelerating

[Sacrecow]

Hello Guys.
I'm new on this forum, so I would like to say Good Morning to everyone.

I have a X6 with N54 engine and I have a problem with engine for almost 3 months.

Car starts immediately without problem. On idle works perfectly without any issues, starts normally when cold and hot, doesn't matter.

The problem occurs when I drive approx 60- 80 on the road, the engine is very loud, like with open pipe exhaust. Also when leave the roundabout and accelerating, rpms drops for about 200 and come back, engine working very bad.
Also when I set gearbox in manual mode on low rpm, car accelerating is very jumpy / jerky.
I create a video with the problem.

What was done for try to eliminate the problem:

- regeneration of the WG valves on turbos, because I had occasionall 30ff error with underboost. Also I heard the rattle from this valves. After repair, all is fine and underboost is gone.

- I thought that this issue can be caused by misfire, so I changed the coil pack and spark plugs. I bought Bosh plugs, also tried with NGK 1 step colder iridium, nothing helped.

- because replacing coils and plugs didn't help and I had quite high rough running values in ista I bought and replaced all 6 injectors with OEM brand new with index 12, didn't helped, but after that rough running values are below 60 in ista.

- I checked the lambda values and found the one narrowband probe have too big resistance, and give too low voltage. I replaced them and now lambda is good on all banks. Voltages on the probes are ok.

- replaced all of vacuum hoses.

- checked and cleaned pcv valve on the valve cover. I didn't replaced it because it's fine and hold the pressure. Also, ports inside valve cover are clear.

- carbon on the valves was cleared, didn't help.

- HPFP was checked in ista and seems to be good. Pressure on test was approx 200 bars.
No issue on start, so I thing that HPFP is good.

- In the past I had the problem with faulty torque converter, was replaced with brand new one.

I really have no other idea what else can cause this problem, engine is pretty clean, without any leaks. I checked compression on the cylinders and everything is fine.
No codes on the computer, Ista says nothing.

VIDEO: https://youtu.be/NSe4e1VcgN0

Thank you in advance for any other ideas and happy New Year.

[adm750]

Scarecrow....wish I had some ideas for you, but you seemed to have covered quite a bit. I watched the vid.

would a faulty throttle pedal do this but not set a code....?

Do these have a vacuum controlled exhaust valve and if so, is there any issue with the connection...? I don't know the e70's that well, just tossing out ideas...

[Sacrecow]

Hi, thanks for the post.
I checked the throttle pedal and also throttle body. Pedal have built-in 2 resistors, primary and secondary for control. All of them working properly, I checked it in ISTA.
Yes, e70 also have the flap on the exhaust pipe working on the vacuum. I can turn the flap by the diagnostic tool, so I think it's tight. I tried to manual open the flap and drive for some miles, but this modification didn't change anything. I also checked the vacuum side on the WG valves and they are completely closed on 0,5 bar (about 7 psi).
In the case of work near the WG pressure converters I found that the wire on the coils capacitor is loose, almost completely broken. I soldered them today and will see if anything will change. For me this issue looks like definitely problem with ignition or spark plugs but occur only when the car under load.

If the capacitor will nothing changes in the next step I plan to remove the valve cover and looking for any cracks.

[adm750]

man...I hope you found the cause...!

[Sacrecow]

Yeah, problem solved. Thanks for suggestions. Problem was the capacitor - was broken. I replaced it by new one and car run perfectly now.

[adm750]

[karm1]

what capacitors are you talking about ?