well i bought the o2 sensor because the code that came up on the diagnostic testshowed the sensor before the cat.And after i bought the sensor today, the check engine light went off after reving the engine a few times.And i bought a light weight crank pulley to free some stress of my motor. And was supposed to install the sensor tomorrow but now that the check engine lights off hopefully it wont come on again, im only going to put on the pulley. sorry didnt mean to confuse u, and i asked your oppinion on headers.