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Old 07-13-2019, 07:33 PM
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Gas mileage

So right now my 89 4.2 is only getting about 9-10 mpg which is quite atrocious. Here are specs:

4.2 carbureted
33” tires.
Lift. Maybe 4”?
3.07 gearing
I do all highway driving and can’t figure why it’s so bad. I was hoping maybe the thermostat was running cool and the cpu was dumping fuel in the mix. Apparently engine is running at temp but there is still the smell of gas in the car- even after having been off for several hours. Any ideas or suggestions? Is there a way to install a manual choke/enricher?

And anything outside of the above mentioned? How much will a 3.73 gearing change help? I drive between 1500-2500 rpms and don’t use 5th gear.

Any suggestions would be appreciated. Thanks

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Old 07-13-2019, 08:13 PM   #2
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What's with all the symbols

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Old 07-13-2019, 08:14 PM   #3
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Tune up smaller tires or buy a Prius if you want mpg
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Old 07-13-2019, 08:47 PM   #4
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Crazy said it.

In order of cost....
1- Tune up
2- Drop down to 31" tires or smaller
3- Regear to 4:10, 4:55 or 4:88. 4:88 gears especially if you plan on keeping the 33s.

I get almost 11 MPG with a 6 cyl, standard shift and 3:07 gears.
Jeeps aren't known for their mileage.

Good Luck, L.M.
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Old 07-13-2019, 09:03 PM   #5
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Good fuel mileage was never in the AD, with that being said you could probably squeeze a few more mpg out of it with a proper tuneup... remember your driving a box with wheels



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Old 07-14-2019, 02:54 PM   #6
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30 year old jeep, and you worry about gas mileage? Stick a 2010 chevy v8 in it and you can enjoy 20 mpg. If this is too much work for you, get a Prius.
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Old 07-18-2019, 08:24 AM   #7
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Not trying to be a #@@@ so dont take it that way. I have a Ranch and have always driving 1 ton 4x4 diesel trucks. I need the power for pulling trailers. I understand the trade off, power gives up fuel mileage, like 9-11 mpg and diesel prices. I kind of see my 95 the same way. I bought this jeep for fun and thats what it does. I do drive it regular, 95 miles round trip for work at about 11mpg. 4 inch lift on 33s. It is what it is.
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Old 07-19-2019, 11:01 PM   #8
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I've had my 4.2 for 4 years now and average ~12mpg.
I think your issue is highway driving. With 3.08 gears you'll be in 4th flat out most of the time using all 112 of that horsepower you've got. If your jeep is smelling of fuel you probably have an issue though. Mine used to smell of fuel and would have a hard time starting hot, the carb was leaking fuel into the manifold somehow. Pop your carb off and see if you can see a puddle of gas in the manifold. I just today put on another carb and my hot start issues are gone and it doesn't smell of fuel anymore.

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