When driving my 96 STI 2 hard (iE just before the 7000 rev limiter) my 'Check engine' light briefly flashes on the dash any ideas why??

Its got Apexi ecu and commander, stainless and decat, induction kit yellow injectors and FMIC

 

At a guess your probably getting a high knock count,Whats the count on the commander?

 

im not sure im not too clued up on using it to be honest. Its just a bar reading with no scale isnt it