Cherokee fuel mileage

[bwhite52yes]

I have a 94 Jeep Cherokee that was getting 25 miles to a gallon but is now getting 18 miles to the gallon. I tuned it up and changed the o2 sensor but it didn't help. The car is a 6 cyclinder standard transmission and runs extremely well. My daughter had it for 3 years and I guess she never checked the mileage. I use fuel supplement every other tank of gas. Any suggestions appreciated.

[brainyass]

Here is what I did for my 1993. I was getting 350 miles on a full tank. When my trouble started I would be empty at about 285 miles. I checked to make sure the brakes were not rubbing, causing a drag. I replaced the air filter. New plugs, distributor cap, and rotor button. I replaced the fuel filter, just filled it with super supreme (seemed to help the most). Cleaned the throttle body and CCV valve on the valve cover with carb cleaner. This is where I'm at now and it seems to be getting better mileage. Right now I'm at 165 miles and still at a half a tank. Another side note: my fuel pump used to be really noisy, especially when it was close to empty or on a hot day. I used some Marvel Mystery Oil and it is very quiet. On the other hand, I get no more audible warning if I'm about to run out of gas!

[Carlson327]

Just curious, do you each have 4WD? I have a '92 XJ 4X4 and get about 14 mpg. When I first started keeping track, I got about 15 mpg. Now, with the last fill up, I'm getting about 13.25 mpg. I have relatively new plugs (this past summer), cap & rotar (approx 1 yr), and spark-plug wires (approx 1 yr). Fuel and air filter are somewhat new, too. To be fair, my commute to/fro work can vary with the amount of time I sit in traffic, but this trend in declining mileage has me wondering. Thanks.

[brainyass]

Unfortunately mine is a 2WD Automatic. To conserve gas, I always try to accelerate slowly and try not to use my brakes too much. I try to coast to a stop as best I can to squeeze every last cent out of a full tank, currently $2.45/Gal for Regular Unleaded in Germany.

[bwhite52yes]

Mine is a two wheel drive standard shift. I am a mechanic and just gave it a real good tune job. My daughter had the car about three years and when I got it baxk I couldn't believe the gas mileage. It may be the quality of the gas because the vehicle runs excellent. It does not have any codes stored and I did change the O2 sensor which helped about 2 miles to the gallon. I drive for mileage also. I think I am going to check the injectors.

[sector95]

A 7mpg change is pretty significant.... I have a '00 4WD w/AT and the best I can do is about 18mpg in combined Hwy/City driving...just City and we're talking 14/15mpg...Hwy only runs right at 20mpg or so. Things I would consider if it were my XJ....

Since yours is 2WD, I wowuld take a gander at the front wheel bearings. Have they ever been cleaned, repacked and adjusted? Sounds like you've covered all the other bases fairly well. How about front end alignment? Do the front tires show any weird wear patterns?

What about the motor... I suspect it has well over 100K on it.... hows the compression. As the engine ages it will lose it's ability to maintain compression.

Good luck in your quest...

mike
00XJ

[neon_rt]

I have a '98 XJ w/4.0 and 5-speed.
I usually get 20-22mpg, I would probably get more if I could keep my foot off of the floor. The worst I've gotten was 16 mpg, I had the A/C on almost the whole time and had a lot of City Driving. I use it mostly to commute to work, which is 4 miles of back country road (hence foot to floor and 80mph bonzai runs between corners) and 10 miles of highway (at 60mph).

[Jeepme]

My 95 4.0 stick 4x4 gets a steady average 23 mpg to and from work in mostly highway driving at 65+mph. I can average 24 if I pay attention and shift when the shift indicator on the dash lights up at about 1800 rpm. It has 214000 miles but has been well maintained since it was a pup. I don't let it sit and warm up on cold days which will lower the mpg average as will stop and go traffic. I check tire inflation weekly and run the tires on 35 psi which is the recomended highway pressure for my year. Tire type can affect mileage with an agressive mud type tread getting lower mileage than a street tire. Another consideration is driving style. Smooth and steady as opposed to jackrabbit starts and last minute braking.

I run on any cheap regular gas but I use injector cleaner every other oil change. Another mileage killer would be a silght miss which could be hard to detect, also dirty injectors could cause poor mileage.

[Carlson327]

So, is it believed that there's a lot to be gained by changing the 02 sensor? I bought my XJ with 141K miles on it. Now has 167K. Never done a compression test, but do high-mileage engines commonly get less mpg? I've also checked the brakes, and there's no excessive drag. And I must confess, I don't understand how dirty injectors would hurt the mpg? If injectors are dirty, wouldn't you mostly notice the performance, i.e., cutting out, etc? I know I need to change the oil in the front differential and the transfer case though. I'm bummed that my V8 4X4 Dodge Dakota gets similar if not better mpg than my 6 cyl XJ. Thanks for the comments.

[95xjsport]

I drive 90 miles a day only about 10 city driving, I get around 22-24 mpg I have a 98 xj 5speed with 133000 miles.

[neon_rt]

Dirty injectors will reduce the mileage b/c instead of spraying a fine mist of gas into the cylinder, they tend to drip or not spray an even stream. Gas has to be fully atomized to burn in the cylinder. Gas that drips into the cylinder typically does not burn at all or burns very little yielding no or little power. A cylinder with a bad injector may only produce 50% of the power on the same amount of gas as a cylinder with a good injector.

[Carlson327]

Originally Posted by neon_rt

Dirty injectors will reduce the mileage b/c instead of spraying a fine mist of gas into the cylinder, they tend to drip or not spray an even stream. Gas has to be fully atomized to burn in the cylinder. Gas that drips into the cylinder typically does not burn at all or burns very little yielding no or little power. A cylinder with a bad injector may only produce 50% of the power on the same amount of gas as a cylinder with a good injector.

OK, that makes sense, but wouldn't that eventually clog the catalytic converter, all the gas going out the exhaust? And is there any way to measure this power loss, per cylinder?

The shop I use said not to use gas additives/ fuel injectors, saying they usually don't work, can cause more problems, blah, blah, blah.