I have a mitsubishi outlander with a evo IV 4g63 engine swap, with the stock evo IV ecu, I was able to turn on and drive, check engine light goes off after start.

Went ahead and installed a evo VIII ECU for tuning, everything is working fine, bigger injectors, able to tune, etc. but check engine light is always on, flash on knock works, no codes whatsoever, its really annoying driving with the check engine always on, what is missing? why is the check engine on? ideas to turn it off?

Thanks