Anti-foulers pull the sensor further out of the exact stream just slightly enough to hide the inefficiencies of the catalysts, or lack of them, that would normally trigger a mil code. Pulling sensor's too far out or removing them completely will trigger a mil code for oxygen sensor inactivity. The goal is to stay between both of those.

 

Wow I didn't know about these non foulers. I may pick up a set just to have on hand in case one day I need them (probably not but you never know). I have Kooks LT w/ their high flow H. I've never heard of anyone having CEL issues w/ the Kooks setup though.

 

ya these were a bust on my 05. I put the non foulers in and loaded my stock tune and the CEL came back on after about 30 miles. Threw and o2 and cat code. Its throwing this even with hi flo cats. time to find a stock h pipe now damnit