wildfire

Anybody got any ideas why my car has started to judder when its on boost over 1bar and engine knock goes very high (sometimes 19 and highest was 87, normal running is at 6), sounds like its backfiring at the same time. Driving the car off boost and on low boost things are ok.

Changed the oil, fitted new ancillary hoses and new coolant recently, don't see how this could cause the fault.

Also fit an oil catch tank which i have removed thinking it might of been something to do with that.

Can't see a cracks in the pipes and all connections seem ok.

The car has an Apexi ECU and the following mods, td05, fmic, walbro fuel pump, decat, megane headers.

Air flow reading started at around 1300 and went to 4250mv which i think means the maf sensor is working, could not get the max reading cause of the problem.

I have an air/fuel gauge which is flickering all over the place, strange thing is it flicks around when just the ignition is on making me think it could be the lamba sensor, but that was replaced a couple of years ago and has not covered many miles.

Any ideas