o2 sensor on mj?

where is the o2 sensor located ona 88 mj with the 4.0. i am doing a full back exhaust but i cant seem to find an o2 on the original pipes. where is it or where should there be one?

Look at the exhaust manifold, between where all the pipes collect and the bolt flange for the collector goes into the downpipe. The sensor needs to be able to read ALL the exhaust on RENIX, so that only leaves about four inches of useful pipe to mount the thing...

5-90