02 Sensor questions

[super-KA]

I bought my 240sx with a lot of the exhaust missing, including the part where the 02 sensor plugs in. How would the car run without this 02 sensor? I understand what an 02 sensor does, but being a 1990 model car, I can't see it making as much of a difference as say a new model vehicle built today. I would assume the car would run fine, but the gas mileage would probably suffer some.

[-RJ-]

it would run rich i think, which is bad. running rich/lean destroys your rings

[super-KA]

Just to verify, the KAE's have an 02 sensor on the manifold, and then one more right after the cat, correct?

Also one more thing that would greatly help me out. On the stock manifold there are 3 holes. Two are for air pipes, like EGR, and the other is the 02 sensor bung. Can anyone tell me which of the 3 holes is for the 02 sensor? Everything was disconnected from the manifold when I got it so I'm not sure. I'm welding the 2 air pipe holes as the emissions crap is coming off. Or even easier would be if someone had a pic of an installed manifold on a KAE?
Modified by super-KA at 8:41 AM 9/10/2008