any help please? S1 escort experiencing weird problems about 6-7 psi, get a weird popping/lack of power/bad misfire from the engine bay.

problem is consistent and always happens. Took car to rolling road and they said it was running massively lean and aborted the run. was told to replace the fuel pump.

have replaced the fuel pump with a new bosch item, have checked the system pressure using a gauge on the cold start line and it is running a constant 6 bar all the time even when the problem occurs.

I have a new fuel filter fitted and the car has a motorsport developments evolution chip/separate board in the silver ecu.

when the problem occurs the rev counter does not flicker/drop, I just back off immediately for fear of killing the engine.