so i cleaned the o2 sensors with a wire brush when i put my headers on about 12k miles or so ago, and took them out again tonight to replace them in hopes of returning my millage to what it was a while ago (it has dropped drastically since about early summer). Anyway i noticed that the sensors are caked in soot again and just wanted the opinion of some one more knowledgeable then me as to whether or not this was an acceptable amount of soot for 12k miles or so.

 

oh, and im referring to the the up stream sensors.

 

aka primary o2 sensors