my check engine light is on because of a bad o2 sensor i keep on putting new ones but after a week the same cell comes back up could it be because i dont have a cat and the position of the o2 sensors on the 3 inch pipe that I have be wrong and if i keep on running my car with the light on can these ruin my engine ?

 

Did you do the O2 sensor mod for your test pipe using a spark plug anti-fouler?

 

This one works too (35 bucks shipped):
http://www.audigeeks.com/forums/index.php?topic=2167.0
I had repetitive catalytic insuficiency codes with my HFC and never got one again after installing this spacer.

 

first thing is what was the fault code? and secondly if it was the O2 sensor and you don't have a cat then it wont harm your engine just your wallet if you get pulled for an emissions fail