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Old November 3rd, 2008, 03:38 PM   #1
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Default Need Help!!!! MPG SUCKS!!!!

I'm trying to figure out if anyone has any recommendations for me on how to get my jeep running better! I have a 98 Wrangler with 2.5in lift and 31" tires nothing major but I'm running 3,000rpm at 70 mph and getting like 12mpg. I've owned other jeeps and my friends have jeeps with more extreme set ups and they do better than I do! It's an automatic but I don't think that should change much. I'm in the process of getting ready to put a new in take, high flow cat and cat back exhaust on but is there any other easy fixes???
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Old November 3rd, 2008, 03:40 PM   #2
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Old November 3rd, 2008, 03:42 PM   #3
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HAHA.....I have I never run over 72 - 73 on the highway anymore and nothing changes.
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Old November 3rd, 2008, 03:43 PM   #4
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Old November 3rd, 2008, 03:47 PM   #5
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check your tire pressure and excessive rolling resistance.

try going 65, sometimes it makes a big difference. spengind more money on your vehicle is not the way to get mileage.... to get the money back on that stuff is likely not going to happen. change your spark plugs and wires, air filter and your oxygen sensors... those could be the problem.
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Old November 3rd, 2008, 03:52 PM   #6
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I'm trying to figure out if anyone has any recommendations for me on how to get my jeep running better! I have a 98 Wrangler with 2.5in lift and 31" tires nothing major but I'm running 3,000rpm at 70 mph and getting like 12mpg. I've owned other jeeps and my friends have jeeps with more extreme set ups and they do better than I do! It's an automatic but I don't think that should change much. I'm in the process of getting ready to put a new in take, high flow cat and cat back exhaust on but is there any other easy fixes???
  1. What motor?
  2. Isn't a 98 auto a 3-speed?
  3. You are driving a lifted brick with oversize tires.
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Old November 3rd, 2008, 04:00 PM   #7
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Almost doesn't matter what motor, they both suck on the highway. My 98 4.0 with 3" lift, 31s, and 3.73 gears/5 speed, I rarely got better than 14-15 mpg on the highway, and that had an overdrive.

The 98 auto is a 3 speed, so no overdrive. From your RPMs, you have 3.73 gears.... those were stock with the 4 cyl / auto.

My 97 was a 4 cyl / auto / 3.73s with 31s, it got maybe 15 mpg on the highway also.

How many miles do you have?
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Old November 3rd, 2008, 04:22 PM   #8
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I have the 4.0 I6 and yes it is an auto I picked it up this past summer from a guy who needed cash and new nothing about jeeps!!! So I don't know if the gears were ever swapped or the history of the lift. It only has 45,000 on it.
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Old November 3rd, 2008, 05:55 PM   #9
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Have the MPG's gone down since you bought it?

The 3 speed doesn't help, thats for sure!
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Old November 3rd, 2008, 06:30 PM   #10
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Hydrogen injection?

Just make sure your not at risk of having a backfire...
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Old November 3rd, 2008, 06:47 PM   #11
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Ok so maybe the automatic is the problem......but short of swapping it out for a manual....would I notice any gains by going through the intake and exhaust or doing a gear swap?
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Old November 3rd, 2008, 08:15 PM   #12
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drop ypur speed down to about 62 mph you should see about a 10-20% increase in mileage
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Old November 3rd, 2008, 09:39 PM   #13
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Old November 3rd, 2008, 10:22 PM   #14
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I've gleaned tons of good info from that site over the years.
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Old November 3rd, 2008, 10:25 PM   #15
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Old November 4th, 2008, 07:30 AM   #16
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Trade it for a geo.

Seriously, jEePs suck at MPG.
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Old November 4th, 2008, 07:39 AM   #17
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make sure your torque convertor is locking up, but your MPG sounds about right.

I've noticed decent gains in mpg w/ my pickup truck by never driving over 60 on the highway and shifting into neutral whenever Im decelerating. Probably close to 5 mpg average gains.
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Old November 4th, 2008, 08:31 AM   #18
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Anyone familiar with doing the swap of the automatic tranny with the 4spd out of the Cherokee? Which would bring me from 13/16mpg up to 14/19mpg
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Old November 4th, 2008, 10:02 AM   #19
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The aerodynamics really start to hurt you above 55mph.

I've got a 2002 TJ, 4.0/3spd 31" tires and 3.73 gears. I have been able to manage up to 19.6mpg when I traveled across the U.P. at a constant 55mph. This was with 33lbs in my MTs and 400lbs of gear in the vehicle, half of those miles with the top down. Around town, I can manage about 15mpg on the highway if I keep in the 60-65mph range. Above that, it really plummets. 70-75 towing a 2000lb trailer earns me <10mpg.

So here are my thoughts:

1. Tire pressure - more helps mpg substantially. Try running 30-35psi, when 22-25psi would be "appropriate" to carry your vehicle weight with your particular tires. You're going to air-down off-pavement anyway.

2. Drive gentle. It really helps.

3. Aftermarket exhaust header. I think it bought me 1mpg or so. I suspect a cat-back system would help, too, but I haven't done that yet...still have the original exhaust at 83k miles...

4. Air intake. I don't think I got any real mpg benefit out of my K&N cold air setup.


When it's all said and done, a Jeep is a Jeep. There is only so much you can do, especially with a 3-speed auto. Frequent trips to the pump is the price of admission to the club, I guess.
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Old November 4th, 2008, 10:04 AM   #20
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Anyone familiar with doing the swap of the automatic tranny with the 4spd out of the Cherokee? Which would bring me from 13/16mpg up to 14/19mpg
You could switch the tranny out, but I don't think it is worth it. If you are truely concerned about the MPG of the Jeep and are thinking of major changes to improve it slightly, my advice is to sell it and buy something else.
Gas is cheaper than it has been in a while, when it goes back up you will be right in the sme boat. GO BUY A CAR THAT GETS 30 mpg, don't mess around with changing the Jeep for an extra 2-3 mpg.
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