my check engine light is on bc my O2 sensor. last fall i replaced both sensors and the light never went off and iv been having issues with my gas milage ever since so i know the new O2 sensors didnt do the trick. is there a difference in O2 sensor? and i maybe bought the wrong ones? someone mentioned after market O2 sensors dont always work with cherokee is there such thing as after market compared to stock O2 sensors? where else should i look as well? i need the light off and my gas milage back to normal so i can get the jeep inspected before the new lift goes on. any thoughts or input is greatly appreciated. and keep in mind im learning everything as i go so i might not full understand some responses and havta ask for a more detailed description. thanks everyone.

 

I've heard of some people having problems with Bosch O2's. I replaced the front one in my '99 with a NGK and have no issues with it. I know some guys will only use the Mopar brand, but I couldn't tell you who actually makes them.

 

if you went the cheap route in replacing the o2's then idk. its worth getting the nice 4-wire, heated ones for like 110. have you done other tune up stuff? when was the last time it was on a code reader? sometimes codes will store, but not trip the CEL (i know you said yours was on)...
here is the basics:
(check fluids too)
-plugs
-wires
-cap
-rotor
-TPS
-IAC valve
-CPS
(idk what year yours is, but it wont have the CPS if its a '97+ (i think))
-coil
('00+ i think)
-pull the TB off and hit it with liberal amt. of TB cleaner (suddenly everyone says dont use carb cleaner... wtf)
if you intend to pull the TB, then get the TPS and IAC off and be ready to replace the respective gaskets as they will crack, tear and generally be too worn out to reuse.
after all that you are areally only left with the gas delivery issue- could be a bad pump/filter. they are like 200 though... and this is probably not the source of your frustration.