[strokemycocktus]

Originally Posted by SYT_Shadow

I think the stranger thing is you and audioslave have this issue. There are many, many people running xpipes that have front-biased crossovers and very few complaints.
What i felt driving audioslave's car is a clear problem with the car even though it doesn't throw a CEL. For whatever reason it is not happy at those rpms and I'd bet a bmwlogger log would show similar results to what you see.

Again, I don't really think it's tune related, but something is wrong. Audioslave and another friend both did the same xpipe at the same time with similar miles on their cars, one of them has a alpine tune and the other has an ess tune, the ess tune guy doesn't have the hesitation.

If you are running into CELs then all bets are off, as even shadow codes will upset the ECU. But I guess we'll know better the day we switch tunes on audioslaves car to another tune.

(For the record, i don't have ess or alpine tunes on any current cars).

Every two years I swap my E92 back to the stock tune and xpipe and it's just a downgrade in every sense. A hesitation like you two are describing is not something easy to miss

Yes, it is something strange definitely. Have you had this xpipe with the stock tune for a moment? I was thinking that maybe it needs some special tuning to take full advantage of the crossover being closer to the engine.

I have sent quite some time analyzing the logs and graphs, to me it looks like this:
O2 sensor finds too little oxygen in the exhaust gases at that rpm range for some reason (Lambda about 0.85, afr about 12.5) -> then it causes a fuel trim of usually about -10%~-15% -> then the fuel pulse width is reduced and therefore the engine has less power. All these readings have a significant dip at about 2500 rpm.
I was thinking what factors can cause a rich fuel mixture and basically all can be ruled out - MAP readings look good, airflow looks good as well, so it isn't poor air delivery for sure, fuel trim is negative and pulse width is reduced, so it's rather unlikely that the engine is getting too much fuel. Only things left are poor combustion process and false o2 reading.

I used to get some o2 sensor faults last year, they disappeared eventually but it doesn't mean they are not faulty anymore. Sprak plugs as I mentioned are 25k km old, so changing them will be also a good idea.
Basically I plan to replace o2 sensors and spark plugs, since they aren't that expensive. After that I'll check the logs again. If the problem still occurs, I'll probably ask Alex to prepare a custom tune for me, I hope he'll be able to address this issue.

My bet is false reading from the O2 sensors, since the reaction caused by them reading too rich is inadequate (trimming fuel does not improve engine operation, makes it worse). The only thing that is completely weird for me is that it occurs always and only at 2500 rpm. Not at idle, not at redline, not anywhere else in the rev range.