Mystery gas mileage problem, not normal like other threads

Well here i am wondering whats up, first what i have done.....

Air filter
Plugs 2k ago
Checked the cat today, inside looks brand new adn not discolored but cant see if blocked up
Coolant2k ago
Oil
Scanned with my tech 2 and saw all 4 o2's working but not sure what the readings should look like
Fuel pump was repalced by original owner (dont know miles)

Now here is what i do not knwo about, i had 29's on it before i got 31's and got around 240-280 a tank i think with roof rack and spare on top, i switched to 31 bfg's and began to wheel it hard in deep mud and wheeled it roughly 2 times a week. I hydrolocked the motor twice and i DO have a bearing knock but do not think that would hurt gas mileage this much.

I now get around 160-180 if i am lucky a tank (14-16 gallons), i have tried the driving granny style to not much improvement. My buddy is going to run a complete BG treatement through it next week and i was thinking maybe injector clogged but it still runs goood. I am at a lose here and cannot figure it out, please any ideas befroe i get rid of it and buy another jeep.


i looked through a few old posts from januaury on a local forum and it seems i was still getting 75-80 and sometimes 100-120out of a half tank with 29's (235/75/15's) compared to my 31's, i was wrong in my math, but it still is weird. So basically nothing has changed too much even asince the so called bearing spin 3 months ago. About 12mpg, how is it i read alot of posts and most are getting 13-18 around town on 31's and above with 3:55's still? I don't notice much stress on the motor compared to when my front driveshaft was screwed which i replaced last week along with the front axle. The ebaring has been like this if thats what it is for about 5,000 miles so far, burns no oil nad hasn't gotten worse (knock on wood).

I used to get about 330 miles on a tank with the 30" GSA's on my XJ. When I got my BFG-AT's the mileage dropped to about 280miles per tank. (Highway)

I love my BFG-AT's but it is costing me in the pocketbook. This probably is your problem.

Hope this helps-

Jeff-97XJ.

Hm could be but i got the same with 29 inch snow and mud tires when i first bought it. Stil lwith my 31's i am lucky to get 200 to a tank, not even close

well i have 29 inche tiers and i used to get almost 300 out of a a tank in my 88. i repalced the o2 sensor, i have a cold air intake and a upgraded exhaust and now im lucky to see 150 out of a tank. and this is a new thing. WTF? any suggestions?

Sucks doesn't it,lol. Verdict is in and 170 miles to 17.5 gallons of gas which equals..........are you ready............ 9.8 MPG! WTF is going on here

I get around 12 with 32s on, and i would get around 230 miles a tank. with winter here now im getting maybe close to 170 a tank which sucks for a high school kid. With stock 3.55s and upgraded exhausts

I thought I had bad millage when I went to 32's. Your odo will be off from the change is tires though. When I got a GPS and recalculated with the millage on the GPS insted of what the odo told me I was doing way better than I thought.

At 70 my spedo is off about 7-10mph. Good to know next time I get pulled over. Calculating it correctly I get around 20mpg on the highway, the city driving still sucks though. I thought I was getting around 12 before that.

Big Kev said:

I thought I had bad millage when I went to 32's. Your odo will be off from the change is tires though. When I got a GPS and recalculated with the millage on the GPS insted of what the odo told me I was doing way better than I thought.

At 70 my spedo is off about 7-10mph. Good to know next time I get pulled over. Calculating it correctly I get around 20mpg on the highway, the city driving still sucks though. I thought I was getting around 12 before that.

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Ya i though about that too but 31's shouldn't throw it off that much to be seeing 9.8 or even 11 on a good tank. What calculations did you use to figure all that out?