[Keebler8]

Hey guys I'm in dire need of some help. About a month ago my 2015 550i xdrive (60k miles, running bootmod3 stage 2 93 oct) started stuttering as i would accelerate (about 40-50% throttle).

I replaced all 8 plugs and coils hoping that would solve the issue. It did not. I took it to BMW to diagnose and they said cylinders 4 and 7 were misfiring. They said it was the fuel injectors and wanted $1600 to replace the 2 of them. I just replaced all 8 myself and the problem is still occurring (EU6 plugs, reset adaptations after).

Heres a log showing a medium pull, engine speed plateaus in the middle of acceleration:
https://www.bootmod3.net/log?id=60f9...90c66e0f47fe9e

If anything looks out of the ordinary or wants me to do another log let me know.

Thanks for help in advance!

[ezaircon4jc]

Originally Posted by Keebler8

Hey guys I'm in dire need of some help. About a month ago my 2015 550i xdrive (60k miles, running bootmod3 stage 2 93 oct) started stuttering as i would accelerate (about 40-50% throttle).

I replaced all 8 plugs and coils hoping that would solve the issue. It did not. I took it to BMW to diagnose and they said cylinders 4 and 7 were misfiring. They said it was the fuel injectors and wanted $1600 to replace the 2 of them. I just replaced all 8 myself and the problem is still occurring (EU6 plugs, reset adaptations after).

Heres a log showing a medium pull, engine speed plateaus in the middle of acceleration:
https://www.bootmod3.net/log?id=60f9...90c66e0f47fe9e

If anything looks out of the ordinary or wants me to do another log let me know.

Thanks for help in advance!

Does that mean you coded in the new injectors? This is for the N54, but the procedure is the same:

[Keebler8]

EU6 injectors don’t need to be coded

[Slippy550i]

Could be air metering issue or fuel pressure.

[BettyFkinCrocker]

Your IATs are REALLY high...even for this engine which struggles with IATs in general. You start the pull at 154 which is around what my IATs peak at when doing a 60-130 pull. Your coolant an oil temps are normal so I would look into your aux pump possibly being bad or empty of fluid.

IDK what your ambient temp was, but at cruise I usually see around 15-20 above ambient on the IAT. You need to monitor your log while cruising and see what the IAT is doing. I also wouldn't suggest starting a pull at such a low rpm. My sugestion would be a minimum of 2500rpm (you started that pull at 1700 rpm and had a lot of knock because of it - in addition to the astronomical IATs of course)

As you mentioned, EU6 don't require coding so def not that.

HPFP looks fine.

Try to do a pull from 2500-redline with IATs starting closer to ambient and see what happens then.

[musclesmarinara75]

Originally Posted by ezaircon4jc

Does that mean you coded in the new injectors? This is for the N54, but the procedure is the same:

This guy needs to lay off the Meth...and I'm not talking Methanol

[fstm5]

Bad fuel or incorrect fuel, this is your issue, your rail pressure is crashing

[Keebler8]

My IATs were high cause my coolant was very low, separate issue that was fixed. Turbo coolant line was corroded and leaking.

Can you explain the knocking below 2k rpm? I monitored my knock sensors with ISTA and saw the entire time i was driving they were way above nominal voltage. 4.5-5.5V is normal according to ISTA and when i accelerate all of them were hitting ~20V.

I also noticed my ignition timing for different cylinders ends up being way off when i accelerate. Could this be an issue?

Also I only use 93 octane and have filled up many times at different stations since this started happening a month ago.

[BettyFkinCrocker]

Originally Posted by Keebler8

My IATs were high cause my coolant was very low, separate issue that was fixed. Turbo coolant line was corroded and leaking.

Can you explain the knocking below 2k rpm? I monitored my knock sensors with ISTA and saw the entire time i was driving they were way above nominal voltage. 4.5-5.5V is normal according to ISTA and when i accelerate all of them were hitting ~20V.

I also noticed my ignition timing for different cylinders ends up being way off when i accelerate. Could this be an issue?

Also I only use 93 octane and have filled up many times at different stations since this started happening a month ago.

Get a log with lower IATs so we can rule that out and see what things look like. Also try to make sure your foot is all the way to the floor. You never hit 100% accel pedal on that log

Its typically normal for some variation in the timing between cylinder and it should "level out" the closer it comes to redline. "Normal" variation is usually a few degrees, maybe 1-4. Timing in that log looks somewhat normal though it looks like maybe you were losing traction around 40mph/2500rpm because it pulled all the timing.

I took a screenshot of the section in your log where knock was occurring. The other line is your engine speed.

Where you fill up or what you fill up with isn't too relevant in this case. You'll need to test with e85 or octane booster to definitively rule out an octane issue.

Blk550i Where do you see fuel pressure dropping? HPFP maintains the target fuel pressure throughout the entire pull. Also, poor fuel quality would not cause a fuel pressure issue. It would just cause misfires/pulled timing.

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[Keebler8]

BettyFkinCrocker I took it to another BMW dealer and they diagnosed it correctly this time I believe. Transfer Case failing, pulled the fuse for it and the stutter went away. Have to get a quote for a repair for it. BMW wanted 7k to replace that and the cracked Guibos on the drive shaft.

[BettyFkinCrocker]

Originally Posted by Keebler8

BettyFkinCrocker I took it to another BMW dealer and they diagnosed it correctly this time I believe. Transfer Case failing, pulled the fuse for it and the stutter went away. Have to get a quote for a repair for it. BMW wanted 7k to replace that and the cracked Guibos on the drive shaft.

Ah, that would def explain the timing being pulled.

However, the knock in that log would be unrelated to the TCase. So get another log once you get that Tcase etc replaced.