Ok so I been chasing this misfire for 6 months. First here's background on my car...

vf43, step colder NGK .030 gap, sti uppipe, sti intercooler, 3 port GM bcs, catless downpipe, cbe, 2015 top feed sti injectors, walbro 255 fuel pump, stock clutch and stock flywheel,tuned by torqued performance...

so so here's my problem.

i keep getting this stupid p0304 cylinder 4 misfire on WARM starts only. And it's when I'm clutch in and thrown in neutral coasting at parking lot speeds and sometimes at idle, but again on warm starts only. Boost is smooth and strong at 20psi with no hesitation.

I replaced these already....
MAF sensor
o2 sensor
spark plugs
swapped coil packs (STAYS cylinder 4 misfire)
fuel filter
crank and cam sensors
cleaned grounds
compression is at 150 all 4
leak down at 8%
and I couldn't find a vacuum leak....


So im stuck guys I have no idea what else to check. You think it may be a VAC leak that I just couldn't find and over looked?

 

how many miles on your car? Valve adjustment done yet?