o2 sensor 1 or 2?
 

So here is my problem I have a 98 accord I bought used from a kid who had replaced the engine with a 2.3 vtec which I am pretty sure didn't come with it originaly. It has been running pretty rough and my novice troubleshooting skills have brought me to the o2 sensor. My problem being that I am not sure if a 2.3 vtec is supposed to have one or two o2 sensors because for the life of me I cannot find a downstream to replace the existing one which is tapped directly into the cat. For a 2.3 all I can find is the upstream which is in the manifold. However when I search for o2 sensors for simply an Accord there are both up and downstream. I wonder if the downstream he left there just to fool IM tests or what.

So the basic question is does a 2.3 vtec have one or two o2 sensors?

The F23A1 motor has two oxygen sensor; a primary which is located at the bottom of the exhaust manifold, and a secondary, located in the convertor.