I have a 2 door auto with stock 3.73s and 35in KM2s (actually around 34s) and i avg about 10 miles to the gallon. The dash mpg reads 14.5. I have the superchips flashpaq and programed it for the "35s" with the 91 tune on it. It is all city driving and i dont drive erratically or anything and i usually go with the turtle start. Why is my dash mpg off? and why am i getting such poor mpgs?

 

First things first. Have you checked your speedometer versus a GPS? If not, do this and then "dial in" the tire size in the Superchips.

 

yes i did used two phones to double check

 

Auto, 35's, stock gears. No big surprise.

You are constantly lugging the engine, giving it more gas to get you moving, and more gas to keep you moving.


Lots of posts about the dash gauge not being very accurate. Why? Dunno. Manually calculating is always more reliable.


For the Flashpaq - I gained around 3mpg freeway with the 87 tune. Maybe .5mpg better around town. Doesn't surprise me that you aren't showing any miraculous gains with your all-town driving. (I went to the 91 tune with 91 fuel for two full tanks. Performance was actually a bit worse for me. Not sure why, when most others are reporting better performance, but not worth continuing to pay for that gas for me...)
Auto, 5.13's, 33.5" actual height maxxis bighorns, 18.5-19.5 mpg freeway, depending on speed, 14-14.5mpg in town, depending...

 

Gears.

Also, it may seem counter-intuitive, but until you regear you may get better mileage if you accelerate quicker than you are now. This will get the RPMs up more into the sweet spot of the motor instead of lugging the engine at well below its peak efficiency.

 

Indeed. That gutless squirrel engine needs some gears. Only thing that drives me crazy about my Wrangler is the puny power band. Saving for a truck hemi.

 

Gears are definitely the solution, but for immediate help make sure you have OD turned off all the time, even on freeway runs. Unlocking the converter, gear hunting and torque management are all playing a role in your poor efficiency. Removing the gear from the equation which doesn't place you into the power band will definitely help.

 

why turn the over drive off? What exactly does it do?

 

Overdrive is (in the JK's case) 4th gear. An overdrive gear is technically any gear that's below 1:1, turning the engine slower than the differentials. This lowers engine RPM at highway speeds.

With super-high gearing in the differentials (stock gears and large tires), at highway speeds the engine is already at relatively low RPM. When in overdrive, the engine is well below it's peak RPM and any added load causes the transmission to downshift. It can also cause the torque converter to unlock, reducing efficiency.

The combination of constant gear hunting, unlocked torque converter, and super low RPM reduces mpg.

Turning O/D off prevents the transmission from shifting into 4th gear. Keeping it in third gear will maintain higher RPMs, torque converter lockup, and reduce gear hunting.

 

Turning the overdrive off will help on the freeway keep your transmission from shifting in and out of overdrive on the freeway. I know mine would not let me stay at 65mph on the hwy in overdrive until I put the 5.38 and now she has the power and I can drive 75-80 in overdrive. It stays in the powerband with the higher RPM's.

BTW I have Rubicon, Auto, 4 door, 5.38 and 37" Nitto Mud Grapplers In Chino.

Let me know if you want to stop by my office Central and Schaefer and take mine for a test drive to see the difference.

Chido