2O2orNOT2O2 ?

[93civicvx]

If my '93 VX is getting about 45 mpg WITHOUT the O2 hooked up - runs like crud with it hooked up - appears to be a bad O2, but as someone here pointed out, it could be an wiring issue... What is the gain running with a working O2 ?
Relative question, I know, but all things considered, if I spring for a new O2 $$$ ( if it proves to be defective after TS'ing the wiring and finding the wiring good ), what could I EXPECT to gain mpg wise ? 25 miles ea way to work, flat land, 3/4 55 mph hi-way and 1/4 city driving - East Coast of FL...
Thanks,
Douglas

[JasonG]

To test it, use needles to tap into the wires. Add wire long enough to get through the door to the cab. Oh, tape the needles up so nothing shorts out.
You should see the voltage changs from near 1 to near 4 as it warms up. (Maybe I have it backwards)
Point is if it doesn't change, its a bad sensor.