rear o2?

[spdracer@mail.utexas.edu]

What exactly is the function of the rear O2 on our cars(or more specifically,
96 SE-R).  Reason being.... I'm pretty sure my front one is fried.  I was on a
highway trip and my mileage dropped from about 25 mpg to 15 the next tank.  I
have a techtom so I was watching the injector duty cycle which went up a lot.
The duty cycle is up pretty much everywhere during part throttle; it's idling a
bit rich too.  It seems to be fine during full throttle as the peak duty cycle
hasn't changed.  I know the front O2 is used during part throttle, but does the
rear O2 do anything?  I'd rather not have to spend money on both!

Khiem