Poor fuel mileage
- Thread starter Will Somervell
- Start date
Hummmmmm go back to 31s?
On a more serious note. Regearing would help some.
On a more serious note. Regearing would help some.
No same gears. Was wondering if there was a computer upgrade that would make a little difference. I did have the Speedometer adjusted.
Just trying to get a little closer. I know the only way to get back where we were is to go back to the baby tires. Not turning back.
The only way to regain your lost power and mileage is with a gear swap. No computer flash, cold air intake, throttle body spacer, etc will do any good. You have added a much larger, heavier, and larger tire diameter which killed your gearing. Running 35's on a TJ is no easy modification. Gearing, steering, brakes, differentials, etc all need to be improved as well.
What gearing do you have now and what engine and transmission does it have? That info will point you toward the proper gear ratio. Probably not what you wanted to hear but, you are looking at spending from 1200-2000 depending on what you want and/or needs to be done.
What gearing do you have now and what engine and transmission does it have? That info will point you toward the proper gear ratio. Probably not what you wanted to hear but, you are looking at spending from 1200-2000 depending on what you want and/or needs to be done.
nothing except the correct gearing will bring it close to the same power band it had before. Which will result is better gas mileage.
Did you swap the speedometer gear out? If not, your mileage is being falsely reported due to an inaccurate speedometer.
Just incase you haven't done it yet, here's a how-to on the process:
Speedo Gear Change
Just incase you haven't done it yet, here's a how-to on the process:
Speedo Gear Change
From this, I am assuming that the spedo gears were changed out to correct his odometer and speedometer for the tire size change.
To the OP: Going from 31's to 35's is not trivial on a TJ. As everyone has pointed out, there's more to it than just jacking it up and slapping the tires on. A lot of things are contributing to your loss of 7 mpg after the switch. The size and weight of the 35's, increased frontal area from the increase in height and width of your Jeep. Increase in weight of your jeep from additional gear and goodies, probably. (I've seen very, very few Jeeps on 35's that didn't also have a lot of additional weight added from bumpers, winches, armor, suspension, and usually a bunch of other gear stashed in and on the rig.) None of that helps your gas mileage, and all of it adds up to decreased gas mileage.
If you are talking about a computer reflash on a TJ to help with gas mileage, that just makes me go Hmmm...TJ's use EPROM based ECM's. Yes, they can technically be flashed. No, there are none of those available outside of R&D at the factory. You have to use a piggy back system to change the ECM programming. That should give you a direction to conduct research.
Your gas mileage will suck with 35's. It's a fact of life. Even with everything done perfectly, it will still suck. Sorry to be the bearer of bad news.
I have a LOT of cash wrapped up in my jeep. Which includes the full suspension, and a regear. I regeared as deep as my axles would allow, 5.13. And I'm still only running 33's.
Do I want 35's? Yep! But I'm not willing to sacrifice the reduced power my TJ has now.
To properly run 35's means lots of time and money. Which also means an upgrade in brakes.
Do I want 35's? Yep! But I'm not willing to sacrifice the reduced power my TJ has now.
To properly run 35's means lots of time and money. Which also means an upgrade in brakes.
And I HAVE all that. It's the whole power thing that prevents me from pulling the trigger. And believe me, I WANT to do it bad.
Advance Adapters or Novak would be more than happy to discuss that issue with you.
They have several solutions that directly address a lack of power in a TJ... Sorry, about half kidding. If MOPAR had put a nice, small V8 in the TJ, even for only a couple of years it would have opened up a whole new world for us.Besides that...I drive an SE. What's this power thing you are talking about!?
No computer upgrade or reprogram is going to do anything at all for your problem. The real problem as well described above is your new tire's larger diameter has substantially thrown off the overall drivetrain gearing ratios. The engine RPMs are now much lower at the same speed they used to be with the smaller diameter and lower engine rpms means lower engine power. So now your 1st gear feels like 2nd gear and 5th gear (I don't know what transmission you have actually) is now all but unusable.
Your mpg problem is caused by your engine lugging... running at too low of an RPM. That may sound counter intuitive but the engine RPMs have to be high enough for the engine to work efficiently. Otherwise we could all drive around at 500 rpms all day which you can understand doesn't work. The bigger the tire diameter, the higher the engine RPMs have to be. Lower engine RPMs that are high enough to easily turn 30" tires aren't high enough to turn 35" tires.
There's a very easy fix for both the loss of power and mpg.... have a 4x4 shop regear your Jeep axles (both) to a lower ratio to bring the RPMs back up to where they were before you installed those huge 35" tires. With my own 35" tires and 4-speed automatic, not even the 4.88 gears the previous owner installed were enough... I had to recently regear to 5.38 to get the engine RPMs back to where they need to be. What ratio would be correct for your TJ depends on your engine size and transmission type. What engine do you have and what transmission? And what model year Jeep do you have. And it's not cheap to have your axles regeared, a ballpark will be $1500 though some shops charge less and most will try to get more than $1500 if you let them.
Advance Adapters or Novak would be more than happy to discuss that issue with you.
Besides that...I drive an SE. What's this power thing you are talking about!?
Uh, ... https://wranglertjforum.com/threads/mopar-hellcat-crate-engines.7497/
I used the app on my iPhone waze to use until my gear came in after install it was right on
Going back to the 'baby tires' is not the only way. Regearing would be preferable if you want to keep the 35'" tires and have a decent power band, as described above. Still waiting to hear what year TJ, engine size, and transmission we are talking about...
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