02 sensor q's
 

Other than the 02 sensor that's located back near the cat, I saw what looked like another 02 sensor coming off the first header near the Y-pipe flange. I'm guessing there's also one at the rear header...

At the moment, my car is running all the symptoms of a bad 02 sensor...****ty mileage (I calcuated about 13-15mpg last tank), running rich (fuel smell) and funny acceleration sometimes. I pulled out the 02 sensor by the cat, and it was covered in gas soot...so I'm pretty sure it's gone. I'm also replacing my Y-pipe, since the stock one is rusted solid. (already have my WSP pipe)

overall questions - What are these other sensors?
I've been running rich for a few tanks now...do I think i've damaged my cat or any engine internals?

i was hoping just to replace that one sensor, maybe run some engine cleaner and this problem would be over with.

engine internals are likely undamaged.
cat is probably still ok , don't worry about it until you have an emission test or another problem.
there is only 1 o2 on the car.
I think that california cars had a temperature sensor on the exhaust, but I may be WAY wrong on that.

O2 is not used until the engine is warm. If you have problems during warmup (about 5 first minutes), THEN its the TPS Throttle Pos sensor problem. Clic on, check out:
http://www.cardomain.com/memberpage/748507/6


After warmup, TPS info is bypassed, engine relies on O2. Autotranny uses still TPS to check for driver heavy toe requests...

Check out Sparkplugs.com for the 02 sensor. Its cheaper I find and its basically OEM replacement without the Nissan label on it.

I had the o2 sensor problem for the longest time, now its taken care of and the car runs perfect. Engine internals shouldn't be affected because you've been driving with a crappy o2.