Already done twice with injector cleaner.

Just reading all the BS about mileage. The only real way is to fill the tank the same all the time. Then make some notes about outside temps, wind direction, interstate driving, or whatever U R satisfied with the same resuts. Then average all the miles vs gallons. U will B surprised at the results. Also some of us are in love with our special brand of gasonline, and that should be considered also. Remember the old SHELL ad,,,,,,U can go farther SHELL w/platformate

I track my mileage fairly close (just concerned with avg mpg) no city hwy and i get just over 16 mpg in my 97 neutered Cherokee with 152k miles on it.

All gasoline is the same, It all travels the same pipes and then is distributed to gas stations. The only difference is the additives they put in. If there is an additive to make you go further I wish it could be store bought! So i'm calling a BS on SHELL

I get 14 city 16 highway on 5 cylinders (first is dead due to a cracked head gasket, no I'm not driving it.)
I use Lucas fuel cleaner on ever tank. Really felt a difference since I got it.

Bump

of the 3 stock ones i have with 225 or 235 tires on them i get between high 19's hiway on average with all three..... 2 99 models and one 00 model.
Highest i have seen is 23.1 and that was only once.

I have a 01 with 69K and a scangauge 2 in it. Just got back from a round trip to Florida towing my 2000# boat. Got 21 heading down and yesterday with a hugh tailwind,got an incredible 25 all at 70 mph. Other than that p0303 code,and it's associated rough running, I'm happy.

CHECK YOUR BRAKES AND BRAKE FLUID.
I had a 95 toyota truck that went from 32-35 mpg to 18-20... my caliper froze on my front drivers side...

Apologies if I'm nagging, but any information would be much appreciated

I am getting 3 mpg city and 10 hwy I don't see what you guys are complaining about

From what I've read on here and other Jeep sites, 22 is exceptional. I get about 19 on the highway and I think mine is better then average.

For getting the O2 sensor out, soak the exposed threads overnight with PB Blaster. NOT WD40. You need something that will penetrate into the threads. Not sure of the wrench size needed. But most parts stores will rent you the proper O2 sensor socket. As for the filter, there ought to be an external fuel filter near the fuel tank. Look under the Jeep and find the fuel lines from the tank. One is a return to the tank, the other should have a filter inline. If you are unlucky enough to have the internal tank filter only, then you'll need to drop the tank.

Then I have two exceptional Jeeps. My 95 ZJ with the 4.0, auto, 3.73s and 31s on 3" lift gets 18-21 avg depending on time of year. My daughter's 90 XJ with 4.0, auto, 3.55s and 235/75-15s and no lift gets 21-25 avg. You will get lower MPG in the winter than summer. Cold air is good for HP, not for MPG, and vice versa. A lot of MPG differences can be attributed to driving habits as well.

All gas is not equal, In the Houston area only in my experience with 2+yrs of gas milage recorded @ 2 tanks a week. I got the lowest gas milage by far from Chevron gas, it would drop by almost 2 mpg everytime I filled up there. After 4 tanks I have completely sworn off their gas except for in a extreme emergency.