I may have put a 94 4x2wire after the cat rear o2 inadvertently. There has been no codes thrown or ecu light to indicate a problem but the mpg seems to have dropped substantially. Is this possibly a result the wrong rear o2???

 

Unplug O2 report results.

 

rear o2 is supposed to be only to tell if the cat is working and not really affect anything.

 

correct.