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Unread 06-21-2011, 06:26 PM   #1
roertw006
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2004 KJ Liberty 
 
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Location: , Kansas
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Horrible gas mileage!!!

I've been getting some of the worst gas mileage I've ever had in my liberty lately. A quick check of the tire pressures(I should have known better) provided me with a 2-3MPG bump, but that was still putting me in the 12-14MPG range in the city(something that some Jeep owners usually get, but I have never gotten before). I make it a point to be light on the gas because I am in college and am your typical broke college kid. I also changed the spark plugs; I was hoping for a big difference after that(they were some of the worst looking plugs I've ever seen), but it didn't really do much for my MPG.

I've checked the air filter, tires pressures, changed plugs, and put a light dose of seamfoam in the tank to clear out any carbon. Am I forgetting something? I should be getting better gas mileage than this!!! Last time I checked my mileage I was sitting at 12 and some change for all city driving.

I used to live in Utah(much higher elevation than where I live now(Kansas)), and I got better MPG there! It wasn't a rarity to get 18-20MPG mixed driving, and I never went below 17MPG unless I was purposefully heavy on the accelerator. I know it was mixed driving in Utah, but I still can't bring myself to accept 12MPG city from my libby at a low elevation(1,000 ft +/-) like this. Any help or ideas would be greatly appreciated!

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Unread 06-21-2011, 07:14 PM   #2
tjkj2002
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You forgot diff services(front and rear),trans service,t-case service,PCV valve,brakes,and alignment in which all will effect mpg's.Use the correct plugs? Gapped correctly?


Other issues are AC use,yes it does effect mpg's either way if you use it or roll the windows done.Being in KS the gas effects mpg's no matter what time of the year it is.


And the biggest waster of gas is that "light foot" driving style,it helps for awhile but then comes the carbon build up from it and bye-bye mpg's.Have a professional induction cleaning done,seafoam is way to harsh for your throttle body and plastic upper plenium.
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Unread 06-21-2011, 07:48 PM   #3
roertw006
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I'll look into diff, trans, and t-case services(hopefully this is where I'm losing the MPGs). I checked the PCV right after I posted and it was fine. My brakes are not dragging either. It may need an alignment, although it does go down the road straight and I haven't noticed any big issues with irregular tire wear.

I'm not sure if I agree with the "light foot driving style" being a waster of gas. Seems to me like the more gas you use... the more gas you use. I've never heard anyone suggest conserving gas wastes gas, and thus, I'll probably stick to conserving gas. Thanks for the suggestions though!
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Unread 06-21-2011, 08:04 PM   #4
tjkj2002
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Quote:
Originally Posted by roertw006 View Post

I'm not sure if I agree with the "light foot driving style" being a waster of gas. Seems to me like the more gas you use... the more gas you use. I've never heard anyone suggest conserving gas wastes gas, and thus, I'll probably stick to conserving gas. Thanks for the suggestions though!
Just look at it this way.................

If you reduce your speed by 10mph it takes longer to arrive so if driving 10mph faster uses 5%-10%% more gas you use about the same amount either way due to the engine running longer if driving slower.

Slowly accelerating wastes more gas as your in the lower gears for alot longer with higher RPM's then accelerating faster to get up to cruising speed faster so you get into OD faster.Again using about the same amount of gas either way if you think about the time aspect.


Then the final factor,slower engine speeds keeps operating temps a tad lower building up more carbon and carbon in the intake track will severly decrease mpg's."Getting on it" once a week will actually break up some of that carbon and keep the build up in check over a longer period of time.You will be amazed at how much better any engine operates when it spends some time in it's upper RPM range then never seeing above 2500RPM's.


Just saying.
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Unread 06-21-2011, 08:42 PM   #5
roertw006
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I think you might want to take a closer look at your math. The "light foot driving style" usually doesn't include driving at a slower speed. It usually just means putting your foot on the gas less to get up to the same speed(usually the speed limit is the target(or slightly above it)).

Having tested different methods and recorded MPGs on many occasions, I have to conclude that "light foot driving method" saves a lot more gas than stepping on it. However, I will give you this: I will probably be a bit harder on the accelerator for a while to try to give the old KJ some exercise and a little room to stretch it's legs. It has been too long since I've had some fun with it(although in its current state I doubt I'll be able to have too much fun). Thanks again for the suggestions.
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Unread 06-21-2011, 09:01 PM   #6
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Check the following:
- do battery cables/connectors show signs of corrosion?
- check for any vacuum leaks, cracked hoses under the hood
- finally, you might want to consider replacing your crankshaft and cam position sensors.

Is your engine light on?
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Unread 06-21-2011, 09:03 PM   #7
roertw006
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Quote:
Originally Posted by Reptile View Post
Check the following:
- do battery cables/connectors show signs of corrosion?
- check for any vacuum leaks, cracked hoses under the hood
- finally, you might want to consider replacing your crankshaft and cam position sensors.

Is your engine light on?
no, the engine light is not on. I recently did a spark plug change and it was on for a few days, but it went off when the air/fuel ratio was corrected.
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Unread 06-21-2011, 09:05 PM   #8
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Did you notice a difference in mileage right after you changed your plugs? Coz THAT can definitely have an impact.
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Unread 06-21-2011, 09:08 PM   #9
roertw006
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Quote:
Originally Posted by Reptile View Post
Did you notice a difference in mileage right after you changed your plugs? Coz THAT can definitely have an impact.
little to no difference in mileage. I used the correct OEM replacement plugs(no gimmicky BS), I gapped them correctly, and everything went smoothly. One factor that may have influenced my MPG was the fact that I was a little hard on the accelerator directly after the plug change because I wanted to test power. Still though, even with the added weight on my foot I can't believe my MPG is at 12!
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Unread 06-21-2011, 09:24 PM   #10
Reptile
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Quote:
Originally Posted by roertw006 View Post
little to no difference in mileage. I used the correct OEM replacement plugs(no gimmicky BS), I gapped them correctly, and everything went smoothly. One factor that may have influenced my MPG was the fact that I was a little hard on the accelerator directly after the plug change because I wanted to test power. Still though, even with the added weight on my foot I can't believe my MPG is at 12!
Well, actually yes heavy foot is going to have a huge impact.
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Unread 06-21-2011, 09:27 PM   #11
bnther36
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You might try checking the tire pressure all the way around. If you picked up a nail somewhere, it'll drag you down. Also, I had it once where one of the back brakes didn't completely release.

Good Luck!
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Unread 06-21-2011, 09:36 PM   #12
roertw006
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Quote:
Originally Posted by Reptile View Post
Well, actually yes heavy foot is going to have a huge impact.
Yes, I know, but not nearly that bad. At a much higher elevation than where I am now I used to gun it a lot and I didn't get that bad of gas mileage. If I really put my foot down A LOT I used to get no lower than 15MPG. A heavy foot makes a difference, but not enough to drag me down THAT much.
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Unread 06-21-2011, 09:44 PM   #13
Boodyrider
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I think what you're saying is that your mileage was better when you drove in an area that does NOT add ethanol to the fuel, and is worse now that you are driving in an area that does use oxygenated fuel.

10% alcohol fuel causes significantly poorer fuel economy.
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Unread 06-21-2011, 09:59 PM   #14
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10% ethanol ain't ****, but you'd definitely feel it if you were to run pure ethanol. Also gas is reformulated in the summer. But it doesn't matter, octane is octane is octane.

At higher elevation, air is thinner so the fuel mixture is adjusted to get the same fuel/air ratio. You don't have a turbo so I would think you'd get better mileage and worse performance.

Bottom line... driving habits. The Liberty is quite a heavy vehicle man.
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Unread 06-21-2011, 10:20 PM   #15
roertw006
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Quote:
Originally Posted by Reptile View Post
10% ethanol ain't ****, but you'd definitely feel it if you were to run pure ethanol. Also gas is reformulated in the summer. But it doesn't matter, octane is octane is octane.

At higher elevation, air is thinner so the fuel mixture is adjusted to get the same fuel/air ratio. You don't have a turbo so I would think you'd get better mileage and worse performance.

Bottom line... driving habits. The Liberty is quite a heavy vehicle man.
In Utah, at higher elevation I noticed less power and worse gas mileage. In Kansas, when I first moved back anyway, it was great because my MPG went up a mile or two and my power was noticeably better too. MPG and performance and tied together at the hip. For the most part(keyword: most part) better gas mileage come with better performance and vice versa.

My point is, I should be getting at least 17-18MPG mixed(highway and city) and my city should be no lower than 15MPG(at the absolute lowest). I know a lot of KJ owners will say "no way! 16MPG is all you can hope for if you're only running on highways," but I have experienced 17-19MPG in Kansas, on whatever type of gas we have here, and I know I can get it again! My concern is not for the type of gas in Kansas, or the altitude, I know these things affect gas mileage, but that is not my concern; the concern I have is for what kind of mechanical problems I'm having with my KJ that is limiting the MPG so much.
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