02 sensor

I am getting about 12 mpg city on my 96. Should I check the oxygen sensor. Is that expensive or hard to remove.

I don't think the O2 sensor will make a big enough difference. It mainly controls fuel trim for emissions requirements...not economy.

I stand to be corrected.

I would try a compression test though, the 4.0s can still run relatively smooth with one dead cylinder, but that may be where you could suddenly lose a few mpg's

How do I do that?

You might want to start simple and do a complete tune-up. Plugs/wires/cap/rotor and a complete fluid change. You'd be surprised how letting these things go can effect a modern computer controlled engine...the computer adjusts just about everything to keep you going and can tune you to this kind of situation...folks start with the fuel system when in reality it is the electrics like spark that should come first...

the O2 sensor would play a role in this too but if your not getting a check engine light or code this should not be the first thing you try...

Did you fix your "sound" from the previous post? If it is indeed exhaust, you milage will drop off. But I agree with b1g, start with a tune up. That is the simplest thing to do first, make sure oyu change the air filter too.

Thanks for the help everyone!