Does a black O2 sensor mean i shouldn't nitrous?
 

I recently changed my tranny with a rebuilt one and in the process went from a catalized exhaust back to my offroad h pipe. when i put the cat exhaust on to begin with i had to replace one of the o2 sensors to get the check engine light to go off. When i put the off road pipe back on, the left o2 sensor was completely black while the right one was still white. The left one is also the new o2 sensor. When i start it up in cold weather the left exhaust smokes a little. Kinda like condensation smoke but it doesn't go away until after i drive a while. The right side doesn't smoke at all. I'm going to be pulling the plugs to replace with colder ones when the nitrous kit gets here, but should i really run nitrous with this problem, and what could the problem be? There is no knocking or missing in the engine and it runs strong all the way threw the rpm band. Just thought I'de throw this question up before i put the nitrous on and possibly blow up my engine.

does your car use much oil?
I would do a compres. test on your motor and dont forget to block open the t.b.

It goes threw about one quart in just over a month. But its also leaking out of the rear main seal. I don't think its burning any at all.

do the comp. test and if the motors all good then run the juice