Thanks for all your comments. Ive been away from this one for a little while, had man flu and knocked me out, had to have a day off work and i can count on one hand how many days ive had off work from being ill. Had to put work off and then catch up a few days later. Anyway, never mind.
Gas readings were ok except the oxygen was a little high when the fault was present. No fault codes coming up though. Airflow looked good for the amount i could rev it. Dropped the exhaust off and after a bit of coughing and spluttering got it to rev to the rev limiter, about 4100 rpm, then after that you could gently rev it to the rev limiter. Put the exhaust back on and same thing, you could rev it to the rev limiter and hold it there bouncing around at 4100 rpm, gas reading was good and oxygen was low. Took it for a drive and it wasnt too bad but had a bad misfire under load, felt like ignition breakdown. This time it logged misfire faults. Changed the two coils and it drove fine. Guessing the coils were breaking down and caused the cat to block slightly. Im guessing the supercharger coming in was creating too much for the spark.
Why did it not log a misfire fault, or any fault for that matter, when it wouldnt drive or rev.
Anyway, thanks for all the ideas. Its all one big learning curve, which i enjoy, its just sometimes the cost (and sometimes the customer) means the diagnosis has to be correct first time.
