Will a bad O2 sensor throw a code?
 

I have no CEL on but my 454 tbi has started to run rich and fuel mileage is falling. I know its a 454, lol. With that said I can smell unburnt fuel coming out exhaust. It also accelerates better if I give it more throttle to open the butterflies more (almost like it loads up a little unless under harder acceleration).

The truck has always seem to run tad rich but now its getting worse. I replaced the coolant temp sensor last year. I have replaced the wires, cap, rotor, plugs, etc. I have never replaced the O2 sensor and wonder if that could be bad causing my problem even though my CEL isn't on.

Any thoughts? Thanks in advance