i just got a high flow cat off ebay and it doesn't have a second o2 bung on it, it just has one on the side were the header connects to the cat.is is it okay to have one welded on the midpiping right where the midpipe connects to the cat right after the flange. cuz i don't want ot mess up the polished stainless steel finish on the cat. or do i have to have both o2 sensors on the cat.

 

you will need both o2 sensors for everything to run propper and besides you will get a check engine light for it anyways. its very easy for an exhaust shop to install a bung for the o2 anyways and the thing will be under the car getting rusted and beat on i doubt you have to worry about ruining the polished steel ..

 

Your vehicle requires an obdII cert cat converter. Vehicles equiped with obdII have an upstream and downstream o2 sensor. If the cat you have is suposed to be a bolt in part, and it does not have a spot for a downstream o2 sensor. Chances are its the wrong cat, and you wouldn't pass smog.
Yes a muffler shop can install a threaded piece so you can put an o2 sensor in, I used to do it all the time, but even with the downstream o2 in place, you may still triger a C.E.L.

 

ok im not asking if i can get a bung welded in my cat im asking will it be the same as running a 02 sensor in my cat if i just put the 02 sensor in my midpiping right after the flange that connects to the cat.