i have checked everything;;ie air in tires,brake drag,oil air filter, no problem with gas. when i got my cherokee 1991 4.0 the milage was 17 now between 8 and 11..the xj runs and starts great no bad habbits..any help will be appreciated..tnx johnp

 

have you checked your air filter? when was the last time you cleaned your throttle body? Also how old are your plugs and wires?

 

sounds like you got hit with winter blend fuel...or you have a issue with your jeep

plugs are cheap...replace them

dirty air filter and throttle body wont help either

i would dare say the winter blend fuel is a big culprit

 

Try a new O2 sensor.

 

I have to say O2 sensor. Too big of a difference for winter fuel to cause

 

Agreed with o2 sensor. Won't always throw CEL, sometimes no symptoms and def poor gas mileage. Pre cat sensor I'd guess.

 

good point...didnt notice how big of drop till i re-read the post

i replaced my upper o2 sensor about a month ago and got about 3 mpg back..along with better idle and it seems to have all around benefits

 

What octane grade are you using?