Hello everyone and sorry if my english is bad
Same problem for me, between 2krpm and 3krpm, when i floor it there is a lack of power, sounds like misfires and then after 3krpm the car just pull normally. Catless x-pipe and E85 Alex Alpine Stage 2 tune. No codes recorded.
Few weeks ago I had to pass emissions here in France so I need to reinstall the OEM x-pipe with an Alex Alpine E85 stage 1 tune. Changed the seals between the headers and the x-pipe and everything was ok, no misfires or lack of power. Passed emissions briantly so after that i wanted to reinstall my catless x-pipe.
So i thought it was the seals. Just put new seals with my catless x-pipe and let the E85 stage 1 tune to see if there are misfire under 3krpm. And there are misfires or everything else. When I floor it, I have a lack of power (and sort of burbles) between 2krpm and 3krpm, and after 3krpm everything is ok and the car pulls hard !
Then put the stage 2 E85 tune.. Same problem.
Test with an other fuel pressure sensor (From an other M3). Same problem.
I will double-check for any exhaust leak.. and maybe test with SP98 fuel.