well just like the subject asks, does putting Mid or premium gas into the KJ instead of regular give you better gas mileage??

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Drop what your doin, and go drive your jeep!!!!
03 Jeep Liberty Limited
4X4

It will give you worse mpg. The kj is tuned to run off of 87. It will run off of 89 or 93 just fine but will need to relearn on that octane. You will get the mpg back but it will not be any better.

Its also a good idea to use 89 whe towing to help keep down pinging.

Ohh, octane does NOT give more power. Many people think that and they are wrong.

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LOST KJ'S
Where are you going???
Current Jeep: 2004 Jeep Liberty
-Atlantic Blue
-Air Ride Rear Suspension ; OME/Rustys Lift ; Powertrax Locker ; Moog Lower Ball-Joints ; 245/70/16 Yokohama Geolander A/T-S's on MOABS ; Flowmaster 50 SUV
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http://www.cardomain.com/id/jeepjeepster

You are right..I race ATVs (quads) and many people think that by adding a high octane fuel like VP113 or 110 that they will gain more power. This is usually not the case, with single-cylinder engines it helps them to run cooler therefore letting them run strong longer, not losing any power. Basically a high octane fuel is to help keep the engine run cooler..especially under load like towing.

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02' Frankenlifted White Sport on 31" TrXus M/Ts

89' 2 Dr. Khaki XJ- Waggy 44's, 4.88s, 35's, 3-link on 5.5" coils.

You can run 87 in it for normal driving. 89 is good for towing or hard driving. If you put in a chip, or get your computer flashed to advance the timing, you should run 92 or higher.

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June 2001 Liberty Limited 4X4
Frankenlift II Premium, Al's Upper Arms, 245/75R16 C Silent Armors on Moabs, RL Skink Super Sliders, Rear DTT, Riddler Diff Cover, Fastman Throttle Body, Profinish-Proglass Hood, Borla Dual Outlet Exhaust, TransGo Reprogramming Kit, APS Stall Converter, 4.10 Gears, B&G Chrysler PCM, Lots of Line-X, etc...

In my racing motorcycle and VW days we found that regular always gave more hp on the dyno till you holed a piston. Like they said above higher octane cools the burn, but decreases available hp some. Stay with the 87.

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No one knows as much as all of us.