Hey guys, trying to see if I'm part of the masses with this or if I'm alone... I drive the highway regularly. I get half a tank for about 90 miles.. Usually about 8 mph when cruising 60-70 mph. Which sucks........... But say I throw on my cruise control at 60 mph. My Jeep will stay at 60 mph for about 8 seconds and then it slowly starts losing speed, then the RPM's skyrocket to get the Jeep back to the 60 mph. This kills the MPG on my Jeep. I am running 35" tires on 17" wheels and a 3.5" lift. Is this just a result of that? I'm wondering if an AEV procal or Superchips could fix this?

Thanks in advance

 

It may help a tiny bit, but regearing should bring back the MPG you lost from adding the 35s. With a regear it should maintain your speed while at cruise control and the tranny would not have to downshift and have the RPM skyrocket.

You will still need the Superchips or Procal to help correct the tire size by doing so it will calibrate your speedometer and bring back your shift points.

Before regearing try using a Superchips or Procal to make your tire adjustments and I am assuming you have an auto trans, turning off the OD button may help w/the SC/Procal but overall a regear would be a better fix....

 

Agreed with previous post. I milked mine since 07, tried Superchips and it didn't do squat. Just regeared to 5:38's and wish I had years ago. Mileage still isn't what it was with stock, I was getting about 17, now I get 13 with my gears and 35's.
PM me if you want further details.
Good luck.

 

Guess its not a 2012. In my 08 I had that problem and it was bc it wasn't geared correctly. You probably should check what your gear ratio is and go from there. That would probably be your best bet.

 

Thanks for the info guys. Was trying to do something cheaper before having to re-gear. I've got 4.10s on my 07 automatic. What gears would I need to get? Will probably try procal before re-gear just to see if it will help any

 

Here's a gear chart to help you decide...I would get 5.13s but you can also consider 4.88s. This chart if for 07-11 JKs...

 

You are driving with overdrive on. This is your problem. Turn it off and you're instantly regeared with a push of a button

Currently with 4.1 gears and at 60mph, you should be at 1680 rpm give or take. The 3.8L doesn't produce enough power at such low RPM to maintain speed. Even with stock tires it feels a bit like it's working too hard. If you regear to 5.13 you'll be around 2100 rpm, which is sufficient to maintain 60mph, and the engine feels much, much happier. Now, if you turn off OD, you'll be at 2430 rpm, which gives you even more power. So, really, yes, you could pay $1500 or whatever it costs you to regear, or you can simply push a button and achieve even a better performance from the 3.8L engine. With big, heavy tires, the more power you can squeeze out of your engine, the better.

 

Agreed that driving with OD off will increase power, but it will also increase RPMs. Wouldn't this make for even worse gas mileage on a long trip on the highway? I mean you might get less power with OD on, but turning it off would sacrific MPG for power right?

 

It seems completely wrong but turning off od is giving me good results. I discovered this when I started pulling my popup trailer. I have consistently gotten 15mpg for years. First trip pulling the trailer (2500lbs) including mountain passes, I get 16.4 mpg which to that point was my best mpg ever. Last week I went to our family reunion in the mountains no trailer this time, kept od off. I got 18.2 mpg calculated by hand. That is 3mpg better than I get running od on level highway. What this tells me is this engine is happiest between 2100-3000 rpm, that is the sweet spot.

 

You will actually gain MPG with OD off, because the engine would run more efficiently. With OD on you're lugging the engine and it will run at 90-100% load most of the time (unless you're going downhill). At such high load the throttle will be opened more, letting in more air into the engine, and soaking it with gas that most will go wasted. You know how you're going uphill and have the gas pedal all the way to the floor, but it doesn't seem to go anywhere? You're just wasting gas there, 'cause the engine is already loaded at 100% and can't go anywhere. You need to gear down and unload the engine... then you won't need to have the gas pedal to the floor. Think of it as riding a bicycle. If you're in too high of a gear, you'll get tired real soon. If you gear down, you'll conserve energy and will pedal more efficiently.