ok, if anyone has noticed, i had a prob with my header leaking at the collector gasket (guy who installed cracked the damn thing). So before this prob. I posted how the header made the check engine light go on....now that i'm sure the system isn't working (due to a leak) the light went out....how did that happen? There still isn't a first cat....just a leak....how did the leak help the system????

 

hmmmm . . . Since all Lancers are cali spec . . . . meaning all O2 sensors are in front of the cat.

The ECU is counting the airflow going too fast through the header and eventually throws a CE light. My only guess it's leaking enough air to fool the O2 sensor like being stock exhaust manifold.