right..! symptoms are .. overfuelling, sometimes running on 4 cylinders sometimes on three, poor acelleration and judders then suddenly whoosh!!! full boost.. checked coil pack and one has a poor spark to the coil pack wen lead removed. does nt stall on the offending lead out but does on the others.. im hoping its a coil pack or dodgy lead spark etc and not a knackered piston . hoping someone can put me straight!!! car is a 1997 wrx sti import . running power fc apexi induction, lightened flywheel, ported headers, heat wrapped headers/ exhaust down pipe .

 

Compression test !