can all the ej20 ecus fit or are they all different for each model? i wans to know if i can put a 1997 wrx ecu to a 1998/02 sti 4 or will only an sti ecu fit the sti4? also any tips on reducing the emissions on the sti 4.

thanks.

 

97/98 are the same physical connectors and it will fit and probably work.. the problem might be that the MAF is different, you will lose the higher rpm limit and the map will be different due to cams etc..

As to reducing emissions, get / borrow a UK centre as it contains a cat, the STi doesn't also renew the Lambda sensor and check for exhaust leaks.