I seen some other things that can cause this, bad cracked,stretched flywheel..cracked exhaust manifold..messes with the o2 sensors and will run rich. Vacum line leak.
Good luck and keep us posted, I have the same problem...mpg's so I will keep an eye on this
PS.. cel on?

 

The smoke is a bigger issue like said above head gasket or burning oil.

But last night when I checked I got 252 on the tank with 2" of lift runnin 30x9.50. Average around 16 mpg. After you figure your smoke issue out I would do a complete tune up if that doesn't help.

 

I'm around 185-195 miles per tank, but I've had an intermittent O2 sensor code. I know I've got to change the O2 sensors and do plugs and drive-train fluids.

 

Around 18, I find it odd that it seems like my cherokee dosent hold as much Gas in it then my others do, but it is also the oldest cherokee I've ever owned being a 97. Maybe a different size gas tank? I'm not sure to be honest but it SUCKS

 

I also found that to be the same problem I'm having with mine...But I believe its because of a different reason, Not to sure yet.

 

between 200-250 for me

 

same with me, but when my gas light comes on, i only manage to get 14.5 gallons in there.

 

When I had my 5spd. About 400 in mixed city highway commuting without even thinking about it. Nailed 24mpg on long road,trips. The auto I own now only going 240ish per tank around town. Highway is,only 20.5 mpg.

 

410 on the highway
220 in the city
1000 in my dreams!
AT,4wd & new tires (which may change my mpg)

 

Maybe there was just two cherokees on the line that they felt like stuffing socks or something in the tank. Thats odd that you can only fit that much in there...I know there was a recall for the fuel sending units in 97 so at least I have a dealership to take care of it if that ever goes bad...which I hope it dosent.

 

My 96 with 4" lift and 31's and 5spd I get 360 miles per tank. I drive all highway

 

i usually get 240 in summer and 180 winter (letting it warm up) the most i have seen was 310 when i went to iowa but there was alot of hills and city where i went. im sure i can hit 400 on a road trip. i used to get 220 before i put the 784 injectors in now i average 240 so there is a little difference, if anyone was wondering

 

I'm not so quick to believe different objectors will improve gas mileAGE. Maybe your old injectors where f'ed up and the improvement would have happened with new or cleans stock ones.

 

well actually i took those out of a neon and a minivan in the junk yard, that were both older than mine. and i did do a test a month before a did the injector swap i cleared my fuel trip and at the end of the month recorded all my fuel addaptives from the drb. then swapped them and did it again the stock numbers were close to 0 a bunch of them +3 and 4 meaning its adding fuel and the neon ones recorded almost all the blocks in the negatives around -5 meaning the pcm is taking fuel away (using less fuel to run the same) so its your opinion but the numbers to me dont lie, even though it is a small difference it is a difference

 

The injectors you took out of the neon could have been new. You have know idea if the po replaced them just before junking the car. The only way I will beleive the injector swap is if someone takes new jeep ones and new neon ones and then does a test.