So I got my dynomax header installed today and it ran great. Nothing like the sound of open header. But I went to swap the oxygen sensor and I ran into a problem. As far as I know, my99 XJ only has 1 o2 sensor. It is the one right after the collector where the stock manifold bolts to the downpipe. But my header has a bung on the downpipe AND on one of the header tubes close to the block. I don't get it! The directions don't say anything about it. Can I just plug this or am I missing something? Thanks!

 

A '99 xj has 2 oxygen sensors, one before the cat' and one after. the one before doesnt really matter where it is located ( header or downpipe ) and the other is just after cat'

 

you have OBD II system so you have 2 O2 sensors. one before the cat and one after...so as long as you have them set up like that, plug all extra holes

 

+1. My '99 has 2 O2's. One before the cat and one behind.

 

Thanks guys. I never got around to looking past the cat to see if there is one down there. So I am going to plug one of the bungs on the header and the downpipe. Will it make any difference which bung I put the oxygen sensor in? Is it better for it to be closer to the block on one of the header tubes or down on the downpipe or does it make no difference at all?

 

Disregard the last post. I just read van island's post closer. I will just install it in whatever bung works best with the wiring.

 

I'd think it best to mount the upstream O2 where it samples all cylinders, not just one.