Unhappy with MPG - looking for ideas

[aldo98229]

@ODDs - Hey Aldo, I know you've been frustrated with your Jeep. Can I please kick you in the nuts too?
@aldo98229 - WTH might as well.

Nah, is all good. See my reply above.

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[ODDs]

You are not the only one who thinks the Jeep looked better with the factory rims and 33-inch KO2s; I do too.

I love the Mopar lift: I love the ride and what I can do on the trails. I was, however, having issues with the steering after the lift and once I got the 35s. Thankfully, most of that was rectified with a Fox 2.0 stabilizer and the steering box TSB.

I still have the stock Sahara rims in the garage. I am very tempted to dust off those rims, downsize back to a 33-34 inch tire, sell the 35s and the retro wheels —as much as I love then, and be done.

I wouldn’t get rid of the Mopar lift. But I think the Jeep will look goofy with the Mopar lift and 33-34 inch tires.

This is how she looked right after she got the Mopar lift, still with the 33-inch KO2s. The suspension has settled down a little since, plus I added a winch to the front. So it might not be too bad.

I personally think that setup looks fantastic! I often pull up that image of your Jeep when looking at new wheels to compare them to 'stock+'. And I haven't found a wheel I prefer yet.

My only desire for finding new wheels is to push them out further, like going to a +10 offset. I like a lot of dish to a wheel. But they are almost all 17", which I feel results in too much rubber with 33's in the Sahara fenders. I tried 1.5" wheel spacers with the stock wheels, but that pushes them out too far and looks a bit ghetto.

At this point I am leaning towards pounding out the wheel studs to put shorter ones in, and having 1" spacers made (or even 3/4" if possible).

 

[Kevin Mojito]

Side note: He has the V6 and that engine likes to have it's RPMs up, that's where it performs the best.

Yes, I have the same. Just Rubi so 4:10's. But it still wants to rev more at stead speed then it should. That's when I bump to manual mode.
I can hold my foot still on the gas ( rpm @ 2500-3000 ) manual mode it up 2 gears, drops to 1700 - 1500 rpm. Instant meter jumps from 7-9 mpg to 19-30 mpg range. That simple. It will pull ( doggy ) low rpm.

 

[beaups]

Actually, you guys got me thinking:

• I was getting 17.5 MPG on my JK Rubicons on 35s, which had 4.10 gears
• To be getting 15.2 MPG on a JL Sahara on 35s with 3.45 gears suddenly doesn’t seem totally out of line

Granted JK and JL are apples and oranges. Nevertheless, extrapolating: if I were to re-gear to 4.10 I’d likely see ~ 17 or 17.5 MPG; with 4.56 I’d probably see ~ 18.5 MPG.

This gives me a good view of the hole I’m in.

You don't getter better MPG (usually worse) with higher (number) gears...physics doesn't work that way...unless you don't recalibrate the speedo and your Jeep thinks you are traveling further than you actually are.

Also seriously doubt your issue has anything to do with your tires/weight/gearing etc...especially considering it came on much after you made those mods. I'd start by comparing speedo and odometer with a GPS. If those match I'd move on to trying to solve whatever mechanical issue you have...binding brake(s), bad O2 or MAF sensor etc.

 

[Whaler27]

I must have missed this. It's probably your gearing.

He didn’t change his gearing between 60 days after lift and tires and eight months later when the fuel economy crashed.

 

[Whaler27]

You don't getter better MPG (usually worse) with higher (number) gears...physics doesn't work that way...unless you don't recalibrate the speedo and your Jeep thinks you are traveling further than you actually are.

Also seriously doubt your issue has anything to do with your tires/weight/gearing etc...especially considering it came on much after you made those mods. I'd start by comparing speedo and odometer with a GPS. If those match I'd move on to trying to solve whatever mechanical issue you have...binding brake(s), bad O2 or MAF sensor etc.

That’s generally true, but in this case the question is whether a small bump in the gearing will cause the Jeep to access 8th gear more readily. The marh will depend on the final gear ratio and how often it’s optimized for better fuel economy.

 

[Deleted member 59498]

Man thought I was bad at 15ish. I have heavy foot though so like you 75 is norm.

 

[beaups]

That’s generally true, but in this case the question is whether a small bump in the gearing will cause the Jeep to access 8th gear more readily. The marh will depend on the final gear ratio and how often it’s optimized for better fuel economy.

A 20% shorter bump in axle gearing that triggers using a 20% taller transmission gear will do precisely nothing.

 

[oldcjguy]

You don't getter better MPG (usually worse) with higher (number) gears...physics doesn't work that way...unless you don't recalibrate the speedo and your Jeep thinks you are traveling further than you actually are.

Also seriously doubt your issue has anything to do with your tires/weight/gearing etc...especially considering it came on much after you made those mods. I'd start by comparing speedo and odometer with a GPS. If those match I'd move on to trying to solve whatever mechanical issue you have...binding brake(s), bad O2 or MAF sensor etc.

Not true. When the gearing is that far out and add the unsprung weight into the mix. The driver normally presses much harder on the gas pedal to get the acceleration he or her is used to and likes for their daily drive. Gearing allows the jeep to accelerate and maintain speed easier. Picture riding a 10 speed bike around in 10th gear all the time. You're going to use a lot more energy to keep up with your friends who are in 3rd and 4th gear just to keep up and maintain speeds. People regularly see their mileage increase when properly regearing.

 

[BrntWS6]

You might look into the Livernois tune. I got a 2-3mpg bump after installing it. They dont advertise it but everyone that has posted in the Livernois thread after installing has shown an increase.

Also the extra 50hp on E85 doesn't hurt.

 

[JoeBanks]

The sudden change would make me suspicious of the black box/brains of your Jeep. Modern vehicles “learn” as they’re driven…maybe your modifications triggered something in its learning process. If that’s the case, it should eventually fix itself.
The change of gas mixtures will also effect your mileage and also require the brains to learn how to compensate for the different fuel’s attributes.

 

[Whaler27]

A 20% shorter bump in axle gearing that triggers using a 20% taller transmission gear will do precisely nothing.

…so you agree with my conclusion that, “The marh will depend on the final gear ratio and how often it’s optimized for better fuel economy.”

 

[entropy]

3-4 without a doubt.

No way jose

In fact you might not even get any back based on my understanding. Depending on your driving style city you might get slightly better MPG?

You are just transferring more torque to the wheels at the cost of speed? So that comes at the cost of running higher RPMs at higher speeds since it trades topspeed for acceleration(freeway).

With the t-case your driveshaft is allowed to rotate slower in 4lo while the engine is a higher RPM. It allows you to convert more of that engine power into torque at the wheels. With re-gearing, your axle shafts are allowed to rotate slower while the driveshaft rotates faster than it did before. It is like riding your bicycle up a hill and shifting to the lowest gear.

So whats gonna happen to the transmission? your first gear will become shorter. so yeah, you'll see 8th. But that's because your top speed decreased....

am I right?

I think of re-gearing most of a performance thing an MPG recovery tool.

 

[Outrun]

No way jose

I was going off the OP numbers. Looks like he should be able to do it.
Woo!

 

[Kevin Mojito]

These are direct injected motors now. They are truly dependent on rpm for fuel. Simple easy test with using manual mode. Drop rpm and mpg's go up. It no longer matters high or low map sensor.
That's what I'm seeing on mine. simple test you can do. Your mileage may vary :-P

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