Diagnose Oxygen sensor problem.

[bruno8747]

Well I got a pratically brand new engine in my car. It has 47k miles on it. But my gas mileage still sucks. The only thing I can think off thats affecting my mileage is the oxygen sensor. The thing is I am not getting any ECU codes and the car runs and drives good just burns alot of gas.

Could It be a bad o2 sensor thats causing the bad gas mileage or something else?

[xfactortype1]

The thing is I am not getting any ECU codes and the car runs and drives good just burns alot of gas.

um....oxygen sensor is cel code 12
and oxygen heater circuit is cel code 43
so probably not

whens the last time you did a tune up.
change your filters, pcv valve, check condition of plugs, rotor +cap, and wires. clean your fuel injectors, make sure your egr ports are clear and clean egr. make sure your tires are properly inflated and car aligned, change your oil.
check the condition of your belts. check you exhaust system for cracks, leaks, and does you exhaust smell like rotten eggs?

i know it seems like alot, but the biggest problem with poor gas milage is usually from neglect of maintainence.
and im not saying you neglect your car, just saying

[bruno8747]

Everything has been done tune up wise. The only thing that was left on the car that could possibly affect gas mileage is the o2 sensor. And the old engine used to burn oil and I am guessing that the oil messed up the o2 sensor or something alone those lines.

[xfactortype1]

well then replace it. whats a few more bucks if your replaced the engine