[EfiniMotorsport]

I keep getting a cylinder 4 misfire on my 09 335xi, FBO, MHD 2+ and index 12's. The car idles fine and has decent accel under mid load but as soon as I try and get into boost I can feel a pretty good miss and then I get a CEL for cyl 4 misfire. I tried swapping the coil to cyl 3 and the plug to cyl but the misfire is still on cyl 4. The plug from 4 looked the same as the rest of them. There's only about 3-4k miles on the plugs and coils. What else could it be besides a bad index 12 injector?

[EfiniMotorsport]

I also did a media blast 3-4k miles ago and my LPFP was low 70 psi during the pull.

[Bimmer_Bro]

Originally Posted by EfiniMotorsport

I keep getting a cylinder 4 misfire on my 09 335xi, FBO, MHD 2+ and index 12's. The car idles fine and has decent accel under mid load but as soon as I try and get into boost I can feel a pretty good miss and then I get a CEL for cyl 4 misfire. I tried swapping the coil to cyl 3 and the plug to cyl but the misfire is still on cyl 4. The plug from 4 looked the same as the rest of them. There's only about 3-4k miles on the plugs and coils. What else could it be besides a bad index 12 injector?

If you have the tools you could move that injector to see if it follows.
The other reason could be a vacuum leak near cyl 4 (bad valve cover or gasket) maybe even an injector seal but that's rare.