Hi all. Thanks for the constructive comments. Yes it is a direction im looking for, i do normally do extensive tests as i dont like to be beaten, but then normally you have some direction, fault codes, spark, fuel, etc, but this looks like it could be something simple yet spend a long time chasing as no fault codes are stored and live data looks ok.

I cant do a drive cycle as its undrivable, its all you can do to move it across the yard. Thats why i attended to the brake light switch fault first as ive had a few vehicles that wont rev or drive because the ECU thinks the brake is applied and it says you cant drive and brake at the same time, lol.

The engine revs up well until the throttle pedal position gets to a certain point, just open slightly, then the supercharger cuts in and it goes really flat with a booming sound in the air box. Airflow reading does not fall off, it increases well until the supercharger cuts in, then stays at that point.

I will do a gas check tomorrow if i get time. Also want to look at the fuel pressure. As far as i know this fault happened all of a sudden.

Looks like im gonna have to spend time on it, if the customer will let me. Will keep you up to date as i do the tests.