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Unread 10-06-2013, 02:56 PM   #1
sgtusmc_nc
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Best mpg mods

What are any and all upgrades or mods I can do to improve fuel mil. For a 78 cj with 3 speed. Jeep is my hunting/daily driver 3 days a week.

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Unread 10-06-2013, 03:02 PM   #2
Matt1981CJ7
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Fill out your profile completely, otherwise we can't make many suggestions.

A thorough tune-up is probably your best bet.

Matt
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Unread 10-06-2013, 04:33 PM   #3
LumpyGrits
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MPG and Jeep CJ's, do not belong in the same sentence.
Whatever you do. You will not see any cost recovery in gas savings.
It's just the price of 'admission' for driv'n the real deal.
LG
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Unread 10-06-2013, 05:27 PM   #4
jeepdaddy2000
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Fuel economy increases come in three categories:
Basic maintenance:
This includes insuring your fuel system is operating properly, ignition system is sound, air cleaner clean, thermostat operating at temp, exhaust system isn't mashed, cat operational, tire pressure, dragging brakes, etc...

Optimization: This can run from free to thousands of dollars depending on what has been done to the Jeep and what your trying to accomplish. Examples starting with the cheapest; bumping the timing, opening the plugs, jetting the carb, installing a fan clutch, re-gearing the diffs to match the big tires you had to have (this is a big one), and of course, slowing down....

upgrades: These usually help performance, many times with a small boost in fuel economy (if the Jeep is driven prudently), but usually won't come close to paying for themselves in the end; Aftermarket ignition systems, changing carbs, FI, different exhaust systems, upgraded cam, transmission swaps.

usually if you start with maintenance and work your way through the cheap optimization list, you can bump your economy up with little or no out of pocket expenses. If course, such things as a tired engine, or poor gearing will defeat you before you get started.
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Unread 10-06-2013, 05:35 PM   #5
LumpyGrits
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OP, what's your ave. mpg now?
LG
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Unread 10-06-2013, 05:35 PM   #6
WindKnot
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LG is right on this. The whole nature of a Jeep is to take you places where you can't get to otherwise. Anything you do to increase mileage will interfere with its "mission".

Even its appearance shouts disdain and contempt for the wind tunnel. The engines are all about torque, and the transmissions and gearing are all about climbing. It carries the extra weight of a transfer case an extra driveshaft and another differential. Sipping gas is not what a CJ is about.

Jeep tried to play the mileage game during the gas crunch. The owners of those Jeeps today are the ones changing out the gears to ones more stout, and even they with their four cylinder engines will tell you they still get lousy mileage.
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Unread 10-06-2013, 06:05 PM   #7
sgtusmc_nc
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Lol thanks, while I'm use to the classic truck mpg of 8-12 mpg. I'm just looking to not be around the 8 range and hopefully more by the 12-15 range
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Unread 10-06-2013, 06:09 PM   #8
rcsutton
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EFI will help mileage & power all it takes is $$$$$$$$$$$$$$$$$$
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Unread 10-06-2013, 08:14 PM   #9
holliewood61
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Only way I've found to save a little gas in my cj is to drive the tj instead. I'm like you in the 8 mpg range but the enjoyment I derive from driving it is worth every penny. If it got 2 mpg I'd just suck it up and put the gas in it
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Unread 10-06-2013, 08:26 PM   #10
LumpyGrits
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Mine gets 14-15mpg on level road and no head wind.
It's carb'd, and PRK smog legal.
LG
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Unread 10-07-2013, 02:18 PM   #11
Balvar24
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I'm pulling 16 mpg on a mostly stock set-up. Not getting in a big hurry helps quite a bit.
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Unread 10-07-2013, 04:53 PM   #12
CJ7KAHUNA
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Quote:
Originally Posted by Balvar24 View Post
I'm pulling 16 mpg on a mostly stock set-up. Not getting in a big hurry helps quite a bit.
Im getting similar results. Best I can figure is 16-18 and thats running a MC2100 and no smog gear. Not getting in a hurry is a huge mpg saver IMO.

EDIT:

I should ad that I don't have an odometer due to my speedo being out at the moment (using GPS for speed). My wife has been driving my CJ to work and back - a little better than 30 miles round trip - and she is getting about 4 days or 120 miles on roughly 6.5 gallons (varies depending on cost per gallon of gas)
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Unread 10-07-2013, 04:59 PM   #13
swatson454
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An optimized advance curve helps a bunch. My buddy has a bone-stock, mid-90s Chevy truck. He installed a data-logger on it that shows what the factory ecm is doing and it shows around 18* of advance at idle and runs a hair over 50* going down the highway.

I'm not suggesting that a Jeep with a six-banger needs those numbers but moving in that direction and away from the FSM specs should show good results.


Shawn
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Unread 10-07-2013, 07:27 PM   #14
86cj74.2L
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Grammys CJ with everything still working smog wise is 16-18 also.
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Unread 10-07-2013, 07:46 PM   #15
superj
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My slightly more then stock I6 get 12 in town and 15 on the highway.

Automatic, 4.5, offenhauser intake, four barrel holley, 3.55 gears, installed today a 2.5 lift with stock tires, and the advance plate in the distributor flipped to 18.

I also set my time and idle with a vacuum gauge so it is properly set for my engine, not set for a variety of pretty close to the same engines.
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