Yep...ANOTHER terrible gas mileage thread
Seasoned Member
Joined: Oct 2009
Posts: 283
Likes: 0
From: Indianapolis, IN
Year: 2001
Model: Cherokee
Engine: 4.0
Well your MPG's do suck, and can probably be better, But just cause you are driving all highway doesn't mean you should have great gas mileage. There are other factors, like how fast you are going, what are your RPM's at your cruising speed, Hills and terrain changes, and ultimately what gears you have. There are alot of variables that all work together that make up your MPGs. The trade offs of swapping up to 4.10 gears is that at higher speeds your gas mileage will plummet due to higher RPMs, but you will see a gain at lower cruising speeds as your engine isn't working as hard.
If you want some quick easy fixes swap O2 sensors and install a highflow Cat.
If you don't want to swap gears, then maybe think about getting some smaller tires.
If you want some quick easy fixes swap O2 sensors and install a highflow Cat.
If you don't want to swap gears, then maybe think about getting some smaller tires.
Member
Joined: Mar 2010
Posts: 204
Likes: 0
From: Portland, Tn
Year: 1991
Model: Cherokee
Engine: 4.0
im runnin 4.5" lift and 32's right now i get 20 mpg, all ive upgraded was the muffler, changed fuel filter, plug wires, dist cap, dist button, and cleaned intake out. dont even have an air filter 
Seasoned Member
Joined: May 2010
Posts: 406
Likes: 0
From: Suffolk long island
Year: 1994
Model: Cherokee
Engine: 4.0 L I6
Originally Posted by Zab243
im runnin 4.5" lift and 32's right now i get 20 mpg, all ive upgraded was the muffler, changed fuel filter, plug wires, dist cap, dist button, and cleaned intake out. dont even have an air filter
Why wouldn't you have an air filter lol its like driving without a gas cap
Thread Starter
CF Veteran
Joined: Jul 2010
Posts: 1,208
Likes: 1
From: Albuquerque
Year: 1999
Model: Cherokee
Engine: 4.0
If you have an AW4 and you're running stock gears with 32" tires driving around in 3rd instead of overdrive should improve your mpg. If you're in OD you will not be in the "power band" of the motor when driving normal and this will cause you to push harder on the gas pedal than necessary- spending more fuel. In 3rd you will be at a higher RPM and even though you'll be reving the motor higher it will spend less fuel. It's sort of the same effect as changing gears. After lifting my '92 (running the same size tires and stock gears as you) I never used OD again. Drove it for 4 years that way and now the new owner drives it that way too with no ill effects. I recommended this out of all seriousness, trying to still help.
There are lots of things that can effect mpg. Just a few small hills in your 15% of non-highway miles can make a big difference compared to someone else that lives in an area where there are no hills at all (like Florida), so you're bound to see some differences. I see a lot of people getting the same mpg as you though, so maybe they live in a comparable terrain as you. Outside tempature, type of gas you use, condition of your battery, and the list of things that can cause poor mpg goes on. I know if I drive my car one mile to the highway and then stay on the highway until i need gas again I can get 3 to 4 mpg better than if I am doing 15% around town and the rest on highway.
So driving around in 3rd will not hurt anything, and if you live in an area that has hills I can bet that your mpg will improve. Let's try it and see if you notice a difference.
There are lots of things that can effect mpg. Just a few small hills in your 15% of non-highway miles can make a big difference compared to someone else that lives in an area where there are no hills at all (like Florida), so you're bound to see some differences. I see a lot of people getting the same mpg as you though, so maybe they live in a comparable terrain as you. Outside tempature, type of gas you use, condition of your battery, and the list of things that can cause poor mpg goes on. I know if I drive my car one mile to the highway and then stay on the highway until i need gas again I can get 3 to 4 mpg better than if I am doing 15% around town and the rest on highway.
So driving around in 3rd will not hurt anything, and if you live in an area that has hills I can bet that your mpg will improve. Let's try it and see if you notice a difference.
I changed the upstream O2 sensor last night (I figured it was about time anyway, even if it wasn't bad or lazy) and put some seafoam through the brake booster line. Seems to be running a lot smoother now. We'll have to wait and see about the gas mileage.
One thing i did notice, however is when I was putting the seafoam in the vacuum line, I noticed some smoke coming up from the engine. Now, I can't be for certain that it was actually coming from there, or blowing from the exhaust under the Jeep, and up through the engine bay. Got me thinking though. What are the symptoms / how do i check for an exhaust manifold leak?
CF Veteran
Joined: Nov 2010
Posts: 1,686
Likes: 1
From: Miami
Year: 1999
Model: Cherokee
Engine: 4.0
One thing i did notice, however is when I was putting the seafoam in the vacuum line, I noticed some smoke coming up from the engine. Now, I can't be for certain that it was actually coming from there, or blowing from the exhaust under the Jeep, and up through the engine bay. Got me thinking though. What are the symptoms / how do i check for an exhaust manifold leak?
Possible that you might have a cracked exhaust manifold? That would explain some loss in MPGs.
Senior Member
Joined: May 2009
Posts: 887
Likes: 0
From: dingmans Ferry, PA
Year: 99
Model: Cherokee
Engine: 4.0
an air filter helps....threw a regular k&n air filter in and i bumped up my mileage up abit, maybe 1 or 2 mpg ....driving from nj to nc i was getting close to 18 mpg with 4.5 " lift and 33s on stock gears and exhaust....start with simple things first...make tires are proper psi, clean air fitler, all fliuds are fresh
Thread Starter
CF Veteran
Joined: Jul 2010
Posts: 1,208
Likes: 1
From: Albuquerque
Year: 1999
Model: Cherokee
Engine: 4.0
an air filter helps....threw a regular k&n air filter in and i bumped up my mileage up abit, maybe 1 or 2 mpg ....driving from nj to nc i was getting close to 18 mpg with 4.5 " lift and 33s on stock gears and exhaust....start with simple things first...make tires are proper psi, clean air fitler, all fliuds are fresh
CF Veteran
Joined: Aug 2010
Posts: 1,168
Likes: 4
From: Williamsport, Pa
Year: 1997
Model: Cherokee
Engine: 4.0L
Thanks. I know sometimes it's hard to tell what's bs and what isn't through the internet. I think we all would like better gas mileage and we're all hoping you come back to the thread and say that you changed out the "thing-a-ma-bob" and you're now getting 5mpg more so that we all can do that. Good luck and keep us posted.
Thread Starter
CF Veteran
Joined: Jul 2010
Posts: 1,208
Likes: 1
From: Albuquerque
Year: 1999
Model: Cherokee
Engine: 4.0
I haven't yet. It's not my DD, so it doesn't get driven that much. Still waiting to take it apart and check for a cracked exhaust manifold. I will definitely start driving in 3rd and see if that makes a difference.
CF Veteran
Joined: Mar 2011
Posts: 1,102
Likes: 0
From: Waterloo, Iowa
Year: 2000
Model: Cherokee
Engine: 4.0
Did you recheck your mileage after you replaced the o2 sensor? Just curious if that helped or not?
Can you hear an exhaust leak or just white seafoam smoke from the engine area. I did the seafoam thing as well and couldn't tell if it was coming from the exhaust manifold/tubing or from under the Jeep either.
By the way, my mileage with 2" lift and 30" tires was 12 mph on my first tank of gas.
(just bought it)
Can you hear an exhaust leak or just white seafoam smoke from the engine area. I did the seafoam thing as well and couldn't tell if it was coming from the exhaust manifold/tubing or from under the Jeep either.
By the way, my mileage with 2" lift and 30" tires was 12 mph on my first tank of gas.
(just bought it)
Senior Member
Joined: Jun 2010
Posts: 703
Likes: 4
Year: 1993
Model: Cherokee
Engine: 4.0
I average 10 to 11 mpg with 31's and automatic with the cold weather right now. Hoping to see some improvement in the summer time
Last edited by pickles; Mar 20, 2011 at 12:05 PM.