i have a ls/vtec motor and didnt pass my first emission tests.. running too rich.. even though i swapped the ls ecu back on... can i slap a sohc ecu on so the car would run lean? is it safe and my car wont detonate or anything else happening

anyone?

NO.

Get an Apexi VAFC and tune the fuel back.
Change your oil.
And get a new PCV valve.