I have a 96 civic with a d16z6 header and down pipe. I have 2 o2 sensors on my 96 dx but the header only has one o2 sensor hole. I am going to get another bunge welded to the down pipe does it matter were it gets welded or does it need to be in a certain place. Also does 1 of the 2 o2 sensor have to go before the other or it doesn't matter.

 

yes it does matter where they go. The primary or the 1 on the header regulates a/f ratio before the cat and the secondary should be fitted right after the cat because they regulate each other. i have been dealing with this 02 problem for while. Correct me if i'm wrong though.

 

How do you tell which goes where. I know the wire on the female end of each connectors are different colors. Also I don't have a cat on the car the header eliminated it. I was thinking about putting the o2 sensor at the end of the down pipe buy the shiftlinkage.