I am thinking of changing the o2 sensors, something I have been meaning to do for awhile. I just don't know how many sensors there are? I bought two (unheated) which is what autozone told me i needed only two, however, I couldn't find anything in the hayne's manual, and i have seen some diagrams online that show four (heated) sensors, two by the manifolds, two further down.
Any help/clarification would be appreciated.