Lately i having backfire problem when i rev it hard after around 6800-8000 When engine is cold. It back to normal after it get hot.
i have replace spake plug, dis rotor, injectors.
i also tried to adjust FPR, VAFC doesn't help too much.
i read my A/F ratio is around 13.5:1 at WOT so i don't think is too rich

My setup:

GSR head/b18b bottom (OBD2)
Mugen ECU (OBD2)
MSD Digital 6.
Stock bottom, injector.
GSR CAM, stork CAM gears
Skunk2 IM
18 BTDC,

What is the problem????

 

are you having any problems running rich at normal temps?
I wouldn't think it's much of a problem when the engine is cold at 6800 RPMs
remember, when the engine is cold, vtec doesn't turn on because of oil pressure.

anothing thing is ur engine is supposed to run rich when the engine is cold so it can burn fuel properly at normal operating temperatures.

let me know man

 

Isn't 13.5 to 1 too lean at WOT? BTW, high RPM on cold engine .

 

keep on reving high on cold engine is going to fu@k your motor

 

Seriously... rev limits change when the engine's cold for a reason

 

I don't mean cold, i mean normal temp.
it backfire at normal.
i tired rich, i tired lean. it just backfire..
it not rev lim from ECU. cuz i still can pull all the way to 8000 (my rev lim).

 

Is it back firing through the intake or exhaust. That would tell you if a valve is hanging/sticking open.

 

also check ignition timing