So recently my 04 (54k) started having the stalling issue while driving. I drove it home, parked it, and started tearing it apart. It is bone stock (except for sohn) with what i would assume are the original coils. So, I 86ed those in favor of new BHRs, MAF is cleaner than a whistle, so next would be the Cat.
The screen (header side) apears to be fine, the cat has no broken peices inside( no rattle while shaking it) but light will not shine through it. I know there is a bend after the cat, but i figured i should still see SOME light. Either way, BHR Midpipe it is!!!

So my question is, the stock 02 sensor is welded to the cat... Is the 02 sensor needed? Ill get a CEL with one, but what would happen if there was nothing there? Plug the hole in the midpipe, then what would happen?

 

The stock O2 sensor is not welded to the cat, it unscrews fairly easily. Nothing bad will happen if you plug the O2 bung on your new midpipe, you'll get a CEL either way.

I have the BHR midpipe. I played it safe and reinstalled the O2 sensor in my midpipe.

You can clear the CEL with an ODB-ii scanner and the Torque app on your phone/tablet/laptop. It'll come back after some time, but at least you're not always staring at a CEL and possibly missing some very important feedback.

 

My o2 is welded in, thats why i asked. I guess what im asking is if there is nothing plugged in the 02 sensor plug, will the car still operate, or do i need to cut the wire off of my 02 sensor and then make some sort of jumper so the 02 harness isnt left open?

 

You removed the O2 sensor cover to discover that the 22mm nut is welded onto the cat? That's odd.

You can just plug the O2 bung as I said before. Many people with a dedicated RX8 race car run without the secondary O2 sensor. You wouldn't need to make a jumper. The primary O2 sensor, the one in the exhaust manifold is necessary for the car to operate properly; the secondary, the one in the catalytic converter isn't.

 

Yeah there is a fat bead around half of it. Idk why either, maybe they replaced it and when they took the old one out some threads came with it..?

But okay, thanks for the info