As title says, Story is my car is at a excellent tuners and has been for a while and they have come across this horrid missfire BUT only when its at 28 psi upwards the car has made good hp which im happy with it but if they wind the boost down to 26 psi the missfire goes?? just to say everything has been changed ie sparkplugs,coil,injectors etc etc, i was thinking maybe an airleak at high boost or would they pick it up via fueling??