Unhappy with MPG - looking for ideas

[aldo98229]

Well whatever you do DO NOT get a 392 and put 37's on it! You'll really hate your gas mileage! I spend more in gas on my Jeep then I did my M6 Hellcat. Well worth it

You must be needing to stop every ten blocks to refuel!

Sponsored

 

[Grand Lake Special]

air filter... air filter....just put a new one in and try it ....I had a squirrel pack a bunch of grass and nuts in my trucks air filter and mileage tanked.. went back to normal as soon as I cleaned it out and put a new filter in place.. cheapest thing to baseline first

 

[Whaler27]

I realize no one confuses a Jeep Wrangler for a Prius, but I’ve been getting only 11-13 MPG lately.

My Jeep is a 2018 Sahara with 8,000 miles on the odometer. It has the V6, 8-speed auto, Selec-Trac. I added a Mopar lift, 35-inch ATs, a Mopar steel bumper and a Quadratec Stealth-10 winch.

The Jeep was averaging 20 MPG. Ten months ago the lift and the big tires came; MPG suffered a little. But fuel economy has taken a dive in the past month or two. I can’t figure out why.

I recalibrated the speedo with the Tazer back when I got the 35s. Now I’m noticing the transmission stays between 3th and 4th gears around town. At 75 MPH it stays on 6th gear; it will go into 7th gear only if it is totally flat or going downhill.

Current tires are General Grabber AT-X; I keep them at the recommended 35-36 PSI. Each tire weighs 67 lbs. They are mounted on Quadratec 17x8.5 wheels, weighing 28 lbs each.

It is depressing to watch the fuel gauge go to empty so quickly.

I am thinking of replacing the 35x12.5 inch tires for 285/75R18 (35x11 inches) ATs mounted on the factory Sahara 18x7.5 wheels (25 lbs each). The narrower tires weigh 60 lbs. I’m guessing that the narrower footprint, and the combined lighter weight of each wheel and tire, might help improve fuel economy.

Has anyone else seen a sudden precipitous drop in MPG like this? Thoughts? Ideas?

Well, it’s obviously NOT the tires or gearing causing the sharp drop — because you describe Running with both for months before the fuel economy went off the cliff.

Assuming you haven’t changed driving style or other variables, Chad’s suggestion concerning the fuel is right on the money. My brother reports a hand-calculated loss of almost 2 mpg when Colorado switches to winter fuel. (He has the 2.0). That and disabling the ESS could explain most of your loss, but not all of it. Is the performance suffering? Any other changes?

 

[CptFloridaMan]

3rd and 4th around town? I’m hitting 6th in the usual 35mph speed zones.
Id wager that a lot of it is the tranny learning the shift points. At highway speeds, Im at least in 7th gear. 8th gear is a stretch though with 35s.

 

[MyDaughters20JL]

Thanks for the replies so far, guys.

Based on your ideas, there are three things I can easily try right away to see if things improve:

1. Change fuel brand. I hadn’t thought of this, but it makes sense. I’ve been buying gas at the local Kroger (called Fred Meyer’s around here) since I moved to the PNW 4.5 years ago. But I am now having a different issue with my Fiat 124 Spider, which uses premium gas, by which the fumes of improperly burned gasoline enter the cabin at idle. I’d been suggested that bad gasoline may have created carbonization in the cylinders. One instance of bad gasoline is suspicious; two data points form a line.
2. Re-activate ESS. I had the ESS turned off with the Tazer. I hadn’t thought about the alternator constantly charging the batteries. But that also makes sense: 99% of my drives are very short, 1-3 miles. This may not be allowing the batteries to fully charge.
3. Check the brakes for excessive binding. I haven’t noticed anything with the brakes. But the Jeep is going for the steering box TSB this week. I will ask the dealer to check the brakes.

I have been buying unbranded gasoline for 20+ years without issue. But since COVID started my drives have become extremely short. Perhaps the combination of short drives and unbranded gasoline has resulted in a bad mixture —pun intended!

figured I'd jump in since we're somewhat local:
Fuel: stay AWAY from ARCO, I have the best luck with either Costco (can actually buy premium for the same cost as regular at 76/Chevron/shell) or chevron as far as keeping my mileage consistent. Also, I've noticed a drop in my mileage about the past 2 months...coincidentally, about the time the weather started cooling off.
really, the first thing I'd do is start experimenting with different brands of fuel..that, alone, could make a significant difference

 

[omnitonic]

I was getting close to 24 mpg combined, stock, measured by the on-board computer, which is close enough for me. I started adding steel bumpers and things, but I was still knocking on 21 until I installed the 2.5" lift and the big ass 315/70R17s. Now I'm getting 17 in normal driving, and 18 when the traffic is really shitty, and I have to crawl.

Wait, what?

That's right. I'm getting better mileage when traffic is bad, and I have to crawl to work. I got the best mileage of all on one commute, when it was so bad I averaged 32 mph for the trip.

Today, when I went on a little road trip to drop the Jeep off to get regeared, it was actually the first time since I've owned the thing that I drove in a 70 mph speed zone. I set the cruise at 74, and only got 16 mpg for that trip.

It's pretty obvious that wind resistance is my enemy. I'm not sure how much of that is from the lift, and how much is from the tires presenting a bigger profile into the wind.

Also, they just switched to winter gas. I always get crappier mileage on winter gas. It has to do with the Reid Vapor Pressure of the blend. They put all kinds of shit into the fuel in summer so it doesn't evaporate as quickly in the heat. In the winter, the cooler temperatures cause less evaporation, so they can use a cheaper blend. Apparently the shit that lowers the RVP also produces better fuel economy. I don't know too much about that stuff. I just used to load the truck and dump that crap in the ground. I read some posters at the loading terminals.

PS - I don't expect to get any fuel economy back when I regear. Maybe a tiny bit, since I am currently raping 1st and 2nd gears to get started, but I don't spend enough time in those gears to matter a great deal. I spend most of my time in 4th gear, and when I get the 4.56 gears going, I'm basically sliding that gear over one slot. I will be turning really close to the same in 6th at highway speed that I turn in 4th now. Regearing will help me when I need to downshift, but driving my crappy 3.45 gears like a 4-speed, even on the 35s, I never need to downshift from work to home. I can just set the cruise and stay in one gear. So I'm not really going to be gaining anything much on fuel economy. It will be a hell of a lot easier on my clutch though, and it will wheel better.

My, I do tend to ramble. I'm not even drunk!

 

[ekim]

mistake

 

[oldcjguy]

I took the Jeep out for a short drive. It appears that setting the tire size from 33.75 to 34.0 inches "freed" the transmission to shift up more readily.

I haven't driven it on the highway yet, but around town, at 35 MPH it was already shifting into 6th gear. So that is an excellent sign!

Using all 8 gears alone will go a long way towards improving fuel economy.

PS - I also turned on ESS and it is kicking in, so the batteries are fully charged.

When you changed tire size the tazer reset the adaptives in the transmission controller, which is why they tell you to do the key cycles and go for a long drive. The TCM will re-learn and, if your driving style has not changed, you'll probably end up back where you were with shifting patterns. I still think it's the city driving and like others mentioned a possibility of a change to winter gas at the gas stations. That's really the only "change" you spoke of. If your pcm isn't throwing any codes I doubt you have an engine or pcm issue.

 

[aldo98229]

When you changed tire size the tazer reset the adaptives in the transmission controller, which is why they tell you to do the key cycles and go for a long drive. The TCM will re-learn and, if your driving style has not changed, you'll probably end up back where you were with shifting patterns. I still think it's the city driving and like others mentioned a possibility of a change to winter gas at the gas stations. That's really the only "change" you spoke of. If your pcm isn't throwing any codes I doubt you have an engine or pcm issue.

Yeah, there are no codes.

 

[Outrun]

You must be needing to stop every ten blocks to refuel!

I should end up with better MPGs with my 392 over my '20 JLUR.

 

[Strommen95]

Regearing is the likely answer. Switching the tire size on Tazer is entirely in your head.


Gears Magazine - The ZF 8HP: It's Shift Strategy, No Problems Here! Adaptive Strategies and How They Affect Your Diagnostic Process

Tazer vs Flashcal vs other JL programmers | Page 16 | 2018+ Jeep Wrangler Forums (JL / JLU) - Rubicon, Sahara, Sport, 4xe, 392 - JLwranglerforums.com

 

[aldo98229]

Yeah, well, re-gearing is not an option for me. I am already having too many problems getting Jeep dealers to honor the factory warranty as it is, with only a dealer-installed Mopar lift.

Just getting a Jeep dealer to do the steering TSB this week took months of perseverance and dogged determination on my part. I am afraid re-gearing would be a bridge too far.

I have trust in Jeep powertrains, transmissions and transfer cases, but its electronics and electrical systems are a different story. If modern Wranglers were simpler and had fewer electronics, or even if I had a fair dealer, I’d re-gear and take my chances. But not with the spotty track record FCA and its dealers have.

At this point, if the only option left to regain some semblance of fuel economy is to go back to smaller tires, I might have to swallow my pride and do that.

Of course this would defeat the entire purpose of having gotten a Mopar lift in the first place. But apparently these are the realities in which Jeep owners are being forced to operate these days.

 

[Outrun]

Yeah, well, re-gearing is not an option for me. I am already having too many problems getting Jeep dealers to honor the factory warranty as it is, with only a dealer-installed Mopar lift.

Just getting a Jeep dealer to do the steering TSB this week took months of perseverance and dogged determination on my part. I am afraid re-gearing would be a bridge too far.

I have trust in Jeep powertrains, transmissions and transfer cases, but its electronics and electrical systems are a different story. If modern Wranglers were simpler and had fewer electronics, or even if I had a fair dealer, I’d re-gear and take my chances. But not with the spotty track record FCA and its dealers have.

At this point, if the only option left to regain some semblance of fuel economy is to go back to smaller tires, I might have to swallow my pride and do that.

Of course this would defeat the entire purpose of having gotten a Mopar lift in the first place. But apparently these are the realities in which Jeep owners are being forced to operate these days.

Has the dealer done the updated computer flash for the transmission? Mine mentioned it stating improved shift and MPG. I sold mine before getting it done, however.

 

[aldo98229]

Has the dealer done the updated computer flash for the transmission? Mine mentioned it stating improved shift and MPG. I sold mine before getting it done, however.

Hmmm...no, I don’t think so. The dealer did check my VIN for any outstanding recalls/updates and found nothing.

I hadn’t heard of this one. What is it for?

 

[Tellurian]

I wouldn’t think a sudden dive would happen so many months after the mods were completed. Could it be oxygen or airflow sensors not functioning properly and more fuel being consumed because of it?

Sponsored