MPG for 06 Rubi Unlimited

WhtRd · 11-19-2008, 05:07 PM

I installed a Banks cold air intake and the Banks Cat Back exhaust. I have gone from the stock 31 inch tires to BFG 33 inch off road tires. It seems that I can watch the gas gauge drop when driving the vehicle. I had the dealer change the computer from the 31 inch to the larger diameter tire to make the mileage and MPH correct. At 30 mph I am dead on with a GPS. Any speed above that I am 5 miles faster on the gps than on the speedometer. I did the calculation based on the new tire circumference and I should be 10% less miles and or mph due to the 33 inch tires. Has anyone done something else to help with mpg? I have not done a chip. When the gas gauge is at half of a tank I am at 95 miles on the trip odometer. Before the lift, bigger tires, cold air intake and cat back I was getting about 250 miles per tank of gas. Any suggestions would be appreciated.

Thanks, and happy jeeping.

**GOLENJEEPTJ** · 11-19-2008, 05:23 PM

First off try to get your profile filled out. It will help in the future for us reading any problems you might entail! You might want to think about regearring after your tire size change! What do you have manual or auto?

WhtRd · 11-19-2008, 05:48 PM

I have the 6 speed manual transmission, stock. I talked with friends at Superlift and the regearing would bring the mph into line. Would this also help with mpg?

Moses2564 · 11-19-2008, 05:49 PM

Take it back to the dealer, and have them re-calibrate your electronic speed sensor. Apparently they did it wrong. There are alternatives, such as a electronic adapter that splice in to your wiring harness, but these can get pretty pricey, around $220. (http://www.quadratec.com/products/16202_000.htm). The upside to these though, is that they can be programmed for two tire sizes, street and off-road, and can be reprogrammed if you re-gear, or increase your tire size in the future.

RVA_TJ06 · 11-19-2008, 08:12 PM

re-install your stock exhaust and intake and use that money to re-gear.

2005LJRubicon · 11-19-2008, 08:49 PM

heck with my rig on 35s an 05 lj rubi with the 6spd. im happy if i get 150 to 175 on a tank. now my speed-o isnt calibrated corectly for the 35s i doubt its that far off. welcome to lifted jeeps.

WILLY348 · 11-19-2008, 09:52 PM

Not a rubicon, but am an LJ here. Last check i was getting 12.8 MPG with 4.56 gears. If you dont like the gas mileage a jeep isn't for you. It's just one of the fun things about owning a jeep

Dmcastino · 11-19-2008, 09:57 PM

Quote:

Originally Posted by 2005LJRubicon

heck with my rig on 35s an 05 lj rubi with the 6spd. im happy if i get 150 to 175 on a tank. now my speed-o isnt calibrated corectly for the 35s i doubt its that far off. welcome to lifted jeeps.

Why would you think its not that far off, your tires are quite a bit bigger, I'd say at highway speeds you are probably quite a bit off. I'm sure you are going a lot farther on a tank than you think since your odometer is correct.

To the OP, dont worry about what your trip says at half a tank, thats a worthless measurement, TJ's have notoriously inaccurate gas gauges, I know my needle has been past dead zero gas on my gage by about a quarter of a tanks worth many times and I have yet to run out of gas. You need to calculate MPG when your speedo is corrected and by setting your trip odometer when you get gas and then divide that number by the number of gallons it takes you to fill up next time you get gas.

CanadianCon · 11-19-2008, 11:44 PM

If you want more MPG buy a honda

2005X · 11-19-2008, 11:47 PM

Quote:

Originally Posted by 2005LJRubicon

heck with my rig on 35s an 05 lj rubi with the 6spd. im happy if i get 150 to 175 on a tank. now my speed-o isnt calibrated corectly for the 35s i doubt its that far off. welcome to lifted jeeps.

even with 4:56 gears, the correct speedo teeth and 35s, im only getting 12mpg. i think i make it to 200 miles once in 3 years of owning it

**tjthorson** · 11-20-2008, 08:17 AM

Somebody did something wrong. The stock rubi speedo is off the other way. Once I went to 33s its now perfect with the GPS - at 60 (better to measure higher speeds when checking accuracy) the speedo reads 60 and I am actually doing 62 by the GPS.

With the stock 31s the Speedo read 60 when i was doing 57. Thats why you "thought" you were getting 250 miles to a tank - the speedo was showing more miles then you actually travelled. I usually get to about 210-220 miles before the light comes on - but I was closer to 240 when the Rubi was on the stock 31s.

incidentally - that 210-220 number is almost exactly what my TJ with 32s on 3.73s with a corrected speedo would get..... More proof if has nothing to do with the weight of the jeep - its more about frontal area and wind resistance.

**fich375** · 11-20-2008, 08:25 AM

I made the same mod install. I still have the stock 31s on there though. The first two tanks of gas I got around 350 to the tank. After that it has dropped off to about 240. I thought they were supposed to increase mpg. Do I have to get a programmer to adjust the air/fuel ratio? Or is it just the nature of the beast? Thanks.

bikerman02 · 11-20-2008, 11:05 AM

I have an 06 rubicon unlimited 6-speed. I usually get between 12-14 miles to the gallon city driving. During the summer I make a trip to WV then MI and then back to FL. I well average about 16 mpg on the highway doing 75. I once average 20 mpg on the trip to WV drafting my dads superduty pulling a 20' enclosed trailer. You don't buy a jeep for the gas mileage if ya care about that buy a toyota camary. I'd rather spend more than twice as much on gas compared to a little car than drive some little sh!t box.

**Bigbob** · 11-20-2008, 12:50 PM

Quote:

Originally Posted by WhtRd

I installed a Banks cold air intake and the Banks Cat Back exhaust. I have gone from the stock 31 inch tires to BFG 33 inch off road tires. It seems that I can watch the gas gauge drop when driving the vehicle. I had the dealer change the computer from the 31 inch to the larger diameter tire to make the mileage and MPH correct. At 30 mph I am dead on with a GPS. Any speed above that I am 5 miles faster on the gps than on the speedometer. I did the calculation based on the new tire circumference and I should be 10% less miles and or mph due to the 33 inch tires. Has anyone done something else to help with mpg? I have not done a chip. When the gas gauge is at half of a tank I am at 95 miles on the trip odometer. Before the lift, bigger tires, cold air intake and cat back I was getting about 250 miles per tank of gas. Any suggestions would be appreciated.

Thanks, and happy jeeping.

First, that is not a real cold air intake. I have a "real" cold air intake, a home-made catback LOL I stuck a Flowmaster under there. I still have the stock gears and you same basic set up, '06 Rubi LJ 6-speed with 33" tires. I also have a lot of armor on mine, more weight than I want. Before my CAI I was getting about 16.4 average checked vis GPS. This was a long trip with a good combo of driving conditions. I have not been on a long trip since so I can only estimate what I am getting now. I predict 17.5-18 avg on a long trip. The real CAI adds a lot of power as well. Before I did any mods when the Jeep was new and stock I was able to get 22 mpg on one tank. But 17-19 was common. You are correct in saying the speedo is off about 10%. I just leave mine be as I normally have a gps unit on and can use it for a speedo.

Ole Yeller · 11-20-2008, 03:30 PM

If you want better MPG, go back to itty bitty tires.