second oxygen sensor removal

[asbestos]

I just installed an OBX header in my 95' KA24DE. Everything fits alright but that damn EGR tube is a bitch but ill most likely just plug it up. Anyways, with the header installed, the 2nd oxygen sensor bung was too big compaired to the small stock o2 sensor. It was the same size as the 1st o2 sensor so I just unhooked the stock small one and screwed in one that I had laying around. I didnt wire it up because i wanted to see how it ran. Well i've been running with the 2nd o2 sensor unwired and im suprised the check engine light hasnt came on.

But what I want to know is the side effects of not having the 2nd o2 sensor wired up? When I first test drove the car, the cat was not bolted on tightly so there was a leak inbetween the cat and header...so it was really loud. So I was test driving and shifted 1st gear at 6000 RPM and in between shifts there was a huge backfire or flame 'pop'. It would do it in between every shift if it was at a high rpm. The reason I ask about the 2nd o2 sensor is that could my car be running rich from not having the sensor hooked up?

I bolted up the cat correctly and there is no more leaks from it but you can still hear the backfire but its alot quieter. BTW i still have the stock SE exhaust and everything else on the motor is stock besides the removal of the y-pipe on the airbox.

ps i live in florida so smog tests are not an issue