Mystery Misfire

[Cheezy]

Alright guys, i need some help. I have a high rpm misfire only in cyl6.
About the car
08 335xi 6at
Dci, chargepipe, vrsf 7" hd fmic, muffler delete, fuel it stg2 bucketless lpfp, mhd v5 e40, xHP Stg2 trans flash.
Misfires only occur after 6300 rpm in 3rd gear or 6100 in 4th gear. Only in cyl6 with no ther codes at all. . Ive recently had the intake valves walnut blasted about 5000mi ago. i changed the plugs to ngk gapped at .020, coil packs were done at the same time as walnut blast, and i did swap out cyl6 plug and coil to see if they were faulty, nothing changed. So i had the injectors replaced with new index 12. Still have a misfire. Logs show fuel rail staying above 2000psi so i dont think the hpfp is faulty. The dme is msd80 so theres a possibility of the mosfet going, but i feel like it would be all the time. I also thought maybe exhaust restriction like a clogged cat but that would mess with the whole bank. And wouldnt a bent or stuck valve give more issues at all rpm ranges?. I have bl tuning coils on the way and thats really my last attempt at a fix. When i reset all adaptations it clears up for about 10 pulls then comes back. I havent had the time to go through and reset them one by one to see which one solves it, but that would be my next plan. Ive read other threads similar to this but it was for a mt car and his issue ended up being dmfw. If any of you experts have had a similar issue and can give a pointer on what solved your issue, let me know. Any suggestions that lead to a solution will be greatly appreciated!!

 

[Jeffman]

I've noticed that issue in the past, but it's not the cause of this misfire. To be honest, when I pulled the plugs to check compression, they were all only finger tight, and I've used a torque wrench everytime I've ever installed plugs. I even found that one of my plugs electrode insulator was broken, but there was no problems in that cylinder either! Crazy engines.

Good to know.
I was thinking a loose plug with gases escaping through the threads could cause a break or reduction in the electrical ground connection between the plug thread and the engine - hence misfire.

 

[fmorelli]

I hate those crush washers. I asked the question because they are one-use washers and can cause problems in my experience. My stuff was pork with a calibrated torque wrench and I had to clean the carbon buildup out of the shafts due to the lack of ceiling with 95770. I moved to the N20 spark plugs with the solid copper washer. I'm sure I'm the only person that believes this but for whatever it's worth LOL

Filippo