FAQ - My gas mileage sucks - Page 4 - JeepForum.com
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post #46 of 108 Old 10-25-2011, 03:39 PM
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I agree .. the 4.0 doesn't have the higher RPM horsepower to get decent mileage with larger wheels at highway speeds, even with the 3.07 gear set, and ESPECIALLY in the auto. I have 3.73's in my 03 TJ 4.0L with 33x12.5 and I regularly get 16mpg .. combo city/highway driving. Keeping in mind, though, that I rarely drive much more than 60mph on the freeway. I find it costs me 1.5mpg to go from average highways speeds of 60mph to 70mph with my Heep. I also have a congo cage, tow package, winch, and all sorts of other heavy things bolted on, fyi, none of which help the mileage either, but damn makes it look good.

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post #47 of 108 Old 11-10-2011, 08:41 PM
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gears are the biggest mileage killer. i'll argue the fact that lower gears like 3.07's or 3.55's are best for mileage. if u want good highway mileage, u wanna find a gearset that matches your tires and keeps your engine at 40% of redline for whatever highway speed u do. 40% is the "sweet spot" of most engines where they are most efficent. variables such as cams, larger injectors, etc can change the "sweet spot". steer away from after market intakes which are usually a waste of money. theres many things that can increase mileage, just be informed before spending money which you may not be sure will help with performance or mileage
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post #48 of 108 Old 12-18-2011, 11:38 AM
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Not speeding when driving a box down the road helps. I tend to drive about 5 over on the highway and notice a big difference between that and 10-15 over....plus the money you save on tickets goes a long way toward filling up the tank!
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post #49 of 108 Old 01-06-2012, 03:00 PM
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I am seeming a 53% increase in fuel mileage with installation of a decent cat back exhaust... Happy heeper....

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post #50 of 108 Old 01-09-2012, 09:17 AM
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Instead of spending all that money on changing the gearing , spend 130 bucks on the Bosch Fuel injectors, 2 friends are getting 23mpg in a Wrangler and 25 in a Cherokee 4.0
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post #51 of 108 Old 01-10-2012, 11:21 AM
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Originally Posted by Dafish
Instead of spending all that money on changing the gearing , spend 130 bucks on the Bosch Fuel injectors, 2 friends are getting 23mpg in a Wrangler and 25 in a Cherokee 4.0
What else have they done to fuel system/CPU to get those results? I have read a lot about them, but it seems as if just those don't do the trick...

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post #52 of 108 Old 02-28-2012, 04:10 PM
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You don't buy/build a jeep because it gets great gas milage. If you want that go get a Honda Civic or something!
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post #53 of 108 Old 02-29-2012, 01:58 PM
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mpg 2000 tj

Originally Posted by WranglerLegend View Post
its impossible to use 0 fuel when coasting, your pistons are still moving, fuel still running through the injectors. but i do have a question...what is the average gas mileage of a 2001 wrangler? mine is horrible, and i drive fairly passively. i think its supposed to be around...what, 18? i get 12. everything is up to specs and all that. or better yet, does taking the top off reduce MPG? i totally didnt even think of that until now...
I have a 2000 tj and it only does 13 mpg....
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post #54 of 108 Old 03-01-2012, 06:56 AM
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I've been averaging 20-21.5 in my 2010 Liberty on my 66 mile round trip commute that is about 90% highway miles. That's cruising at 60-70mph most the way.

Looking more than 3 feet in front of your hood as you drive helps you to ease off the gas as you see traffic slowing ahead. I almost never have to use my brakes or nail the gas if I just anticipate the traffic speed changes.
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post #55 of 108 Old 04-24-2012, 11:50 PM
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I have to say that after reading this, I have been thinking correctly in some of the mods I have been wanting to do to the Jeep...First off in the winter I get between 12-15MPG or about 340-360 Miles to the tank...and here recently I have been getting between 16-18MPG or 405-420 Miles to the tank...I have not done anything to the jeep at all at this point...so this is purely weather change...one of the things that I have thought about doing is adding a 6-2-1 Header set onto the Jeep with a complete Cat-Back Exhaust system, adding a CAI, and changing out the Fuel Injectors...with what everyone is saying...if I do all this, I should be looking at about 35-38MPG!!! this would be AWESOME!!! but really...I don't think so...some numbers are a bit off here...with all those changes, I am anticipating about 23-25MPG in the ZJ...nothing more...I travel 25 miles one way to work and school 99% freeway...literally...and use the CC set to 70MPH every chance I get...just my input...


P.S. Can someone tell me which Bosch FI you are talking about? and are they available for the 94 ZJ?

Last edited by wolfie559; 04-24-2012 at 11:54 PM. Reason: Adding Inquiry to Post
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post #56 of 108 Old 05-06-2012, 12:37 AM
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wow some of you get horrible has mileage im happy with my 9 in the city and 14 high way. hahaha i need a new car.

but...... lets say we were to build a jeep with nothing more in mind that gas mileage you know screw emissions and what not. how would we go about doing that? i was thinking about starting with a cj2a ( because it is smaller and lighter ) with a fiber glass body and an aluminum tube frame. using a turbo diesel engine , tranny, and axles out of a totaled vw tdi. honestly i don't even know if you could get that to work but if you could.....40mpg jeep. think about that.

Are you sure?......

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post #57 of 108 Old 05-10-2012, 12:54 PM
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i like this thread. it proves my 2 years in college paid off some more lol. i took motorcycle and powersports tech. we talked alot about power loss and how come we can only get so much out of an engine. Starts with what make power? believe it or not, HEAT makes power. i found it weird at first considering and engine uses compression but heat is what make the combustion. the reason we cant get more power out of engines it because the material that we are limited to use for making them cant withstand to much heat, we need to cool it. if we had a metal that was super light and could withstand a much higher heat. where could for example take a 200HP engine and easily have it make 350HP and be twice as good on fuel. top fuel dragsters pump water into the cylinders to use the steam to create for power but also help the cylinders to create more heat. im sure there is a metal out there that can withstand the heat but its worth more then our jeeps lol but id we could get a metal like that it would help with for the just engines. It would be good in bearings and breaks. but for now, were stuck with low fuel milage and low HP jeeps. could be worse

if you cant fix it with a hammer, you have an electrical problem!
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post #58 of 108 Old 05-27-2012, 12:01 AM
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Let me add a couple of things. Depending where you live plays a big part on what mods you do to your vehicle. I have been in this discussion in other threads.
If you live in a warm climate all the time enjoy your cold air intake. If you live where it is cold and winter almost 9 months out of the year stay away. You need to atomize the air and need it heated for better fuel economy. I will agree that the smoother the air box and associated items better for the air flow.

You can't stop all fuel flow coasting, the engine will stall and you loose power steering, brakes and vacuum. The engine must rotate at least 500 rpm even with the throttle closed. That is what the tps is set to do and the ecm is set to keep spark and fuel going. The way you can stop fuel is if you have a variable system. you can cut cylinders out but you must have at least one cylinder producing power.

The more air you put in the more fuel used. It is a physics thing. The more heat produced the more friction the less mpg. It is also a physics thing. The only way to increase power is increase the piston bore, cc the heads, short stroke the engine, increase the diameter of exhaust, to a certain point. If you decrease back pressure to much you lose HP. There are other things but all these things increase gas mileage.

Heat is an engines worse enemy cause heat causes friction. What does friction cause....decease in mpg.be it rolling friction, wind friction, reciprocating friction. If you look into Newtons three law's of motion. You see how they apply to loss in mpg no matter how you try to over come it.

Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Or the law of Inertia.

The relationship between an object's mas,, its acceleration*a, and the applied force*F*is*F*= ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector.

In other words angles play a major roll in decrease in mpg be it change in wind or let's say crank position. Some will be changing, but others constant at certain rpm....

and the one we all know and love

For every action there is an equal and opposite reaction.

In other words just these the forces must be over come to increase your mpg and in reality there are to many constants to over come to make a substantial difference in mpg increases.

I spent the better part of my youth and middle life trying to over come these factors. I know of no one that has made a real perpetual engine, though they have come close to isolated types, til you want it to do more work then it can produce. Like moving a car. Or a engine that will over come it's ability to produce an increase in mpg and have less energy then it needs to produce that increase. Which is actually what a perpetual engine is.

When you talk about removing weight or a roof rack your talking about trying to overcome these principles. Anyone that says they can get 20% to 30% over EPA values need to copyright it asap.
It is possible but you are going to redesign and spend more money then it is worth.
I put in another post in the zj forum about VW tdi engines. One made for the USA one for Europe and South America. Made in the same plant but one gets almost 79mpg. Compared to the USA version that gets 45mpg. All thanks to emission and EPA standards.
So no matter what you try to do to a engine made for North America it isn't going to fly, cause once you go for the inspection your screwed.
I could get into aerodynamics and metallurgy but it's almost 1am and I am missing the end of Sharktopus on the Syfy channel.

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post #59 of 108 Old 10-14-2012, 05:50 PM
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I was looking on here to see if some else had the same problem I was having. I have a 2010 Liberty Limited (to the best of my knowledge) everything is stock but the cold air intake and the jets performance chip I. The horsepower is a great mixture with the two parts but I'm still getting 18 MPG and I'd rather have better gas mileage.
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post #60 of 108 Old 10-17-2012, 05:19 PM
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edpmedic. Don't you mean friction causes heat?
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