Re: 3.7L Normal MPG - O2 sensors bad
The front O2 Sensors monitor the fuel mixture, and the rears monitor the effectivenss of the catalytic converter(s). The rear sensors, by themselves, will not cause poor fuel economy, but if the catalyst is bad, and/or the front sensors are lazy or biased rich or lean, FE will be affected. For more info. you can do a search or check out the following thread:
Oxygen Sensors and Their Role in Engine Management--A Primer
05 LX/RT and 06 WK/GCO, (modded similarly) with MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tubular headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 85mm TB, SOS Coils/.060 spark plug gap.