8.4 MPG, Run Great, No Codes, Something Wrong?

[buildbigboats]

Finally decided to ask for your input/help with this...

I've been getting what I believe is terrible gas mileage in my 2006 LJ since I purchased it 8/21. Kind of expect 12-14 MPG. 8+ seems awfully bad for my setup.
Have read threads on the topic here and elsewhere and can't figure out if something is wrong or I just need to accept what I'm getting.

Below is what I think is relevant info for diagnosis:
2006 LJ, 8.4 MPG at last fill up, runs great, no codes, passed IL emissions test in June (OBD check only, no exhaust check).
Based on dash gauge coolant seems to be running about 200deg.
Stock Dana 44 w/3.73 rear and Dana 30 front
2-1/2" lift (based on coil measurements) unknown brand. PO installed.
Duratrac 265/70R17 tires
Wrangler Fix PCM installed 2/22
New fuel pump (DelphiDFG0924) installed 8/22, Fuel pressure read 61psi 11/22
New plugs (XP985) and coil pack installed 10/22.

Anyone have any idea whether there is something I can do/check to see if I can improve my MPG...or do I just need to accept that this is as good as its going to get?

Thanks

 

[Rubiconned]

Sounds like my MPG. Fortunately mine is not a daily driver.
I'd measure it again with the next fillup. You can't judge by just one time.

 

[MikekiM]

I don't know that I can help you diagnose but mine is a DD and I average about 13-16. That's all surface roads with a few off-road jaunts on the weekends. I am a manual, fairly spirited driving..

4.0,
NV3550
4:56
33's
26psi

 

[OldBuzzard]

... 8+ seems awfully bad for my setup...

Is that city, highway, wheeling, or a mix?

My similarly equipped '05 LJ on 33s with 4.56 gears, manual trans, gets 12-15 city, 17-18 highway. It only goes below 10 when wheeling hard.

Can you verify the operating temperature with a code reader? Maybe monitor the O2 sensors, make sure the PCM is switching to closed loop. There are some threads about that here somewhere.

 

[buildbigboats]

Not my DD thank goodness. Highway and city/suburban driving...not often heavy footed...sometime though. This isn't the first time I've checked it. Have gotten similar readings over the past year... just finally am stumped and decided to ask for some feedback.
I believe my OBD reader will do live data feeds. I'll check them out and try to figure out about the closed loop in the PCM

Oh yeah...137k in case that's relevant

 

[deserteagle56]

Something has to be wrong. MY 2006 Rubicon (not an LJ) with a 4" lift, stock 4.10 gears and very heavy LT285/70R16 tires has averaged 16.16 mpg over the past 30,000 miles.

 

[JKP]

Have the O2s ever been changed?

Does it seem down on power? It's possible the cats are plugging up the exh.

On the OBD reader, you should be running around 210 degrees.

Is the fan roaring? A locked up fan clutch will kill gas mileage and power.

 

[Murf926]

There are a ton of variables to fuel mileage. One of them is tire air pressure, another is time spent in 2 wheel vs 4 wheel drive.

I have 35s that I normally run at 25psi with 4:56 gears (I originally setup for 33s) with 5 speed manual.

My last tank with no 4x4 time was all around town driving and I got 16.3mpg.

When I go offroading, it can vary a lot depending on how long I'm aired down vs how long I drive in 4x4.

One of places I go, I can drive as much as 60 miles aired down to 11psi, and only shift into 4x4 (always 4 lo) when I'm doing an obstacle, which is probably only a mile total and probably even less than that. If I do one of those trips per tank full, I'll get an average of about 10mpg on that tank.

I do another trail that is overall steeper and rockier, but with fewer and easier obstacles. On that trail, I only do about 10 miles total, but it's all in 4 low and at 11psi. If I do one of those trips on a tank full, I'll get an average of about 12.5mpg on that tank.

So, I think the reason I get considerably worse mileage on the first scenario is that I'm at 11psi about 6x more miles than in scenario 2, even though very little of that time is in 4x4.

What psi do you usually run in your tires? Have you tried varying that a couple lbs either way to see if your mileage changes?

 

[AndyG]

Lots of good stuff above-

What I’m about to say is not the definitive answer but based on my experience it’s going to be something that I look at on every rig

My LJ is geared properly and was getting terrible mileage and the root cause was the transmission-

The overdrive requires you to increase the throttle opening and the throttle opening is the killer on fuel

you want to start with running a tank with the overdrive off and see if you see a significant change

You need to get it hooked up on a computer and see if the Torque converter is working properly

In my opinion every automatic TJ jeep after 2003 needs to have a cooler and a gauge, service and fresh filter.

You really do need to look at the entire picture though.

I had bigger transmission problems - even with only 57,000 miles.

I’m not trying to scare you I’m just trying to help you see the bigger picture.

 

[DuckNut]

I don't know that I can help you diagnose but mine is a DD and I average about 13-16. That's all surface roads with a few off-road jaunts on the weekends. I am a manual, fairly spirited driving..

4.0,
NV3550
4:56
33's
26psi
View attachment 547724

Is this chart from an app? Something you keep track of?

I am looking for an app to do the same for my vehicles. Currently I use a small notepad and track every expense. I can also tell which station I get the best mileage from (Sunoco)

 

[txbemis69]

have you changed your speedo gear to match your tires and gears? i ask because my fuel mileage was all over the place before i regeared from 3.73 to 5.13. once i regeared and replaced my speedo gear my fuel mileage is a constant 13. doesn’t make any difference if it’s city or highway miles, 13 is all it will do. jeep info. is 06 4.0, 42rle auto, 3 1/2 inch suspension lift on 33 inch mud tires aired to 24 psi. and gears are 5.13. i had hoped for better fuel mileage but it is what it is.

 

[macleanflood]

I got crappy gas mileage in my 97 because of exhaust leaks. Not everything was making it to my O2s.

-Mac

 

[MikekiM]

Is this chart from an app? Something you keep track of?

I am looking for an app to do the same for my vehicles. Currently I use a small notepad and track every expense. I can also tell which station I get the best mileage from (Sunoco)

Yes.. it's an app. Fuelly

I've been tracking all my vehicles for years.

You can log Fuel-up & Service, make Notes that include the odometer reading, date, details include tags, add pictures, location and payment type. Same details for Service with the addition of adding receipts, merchant info, and unlimited services you can choose from a list or free text. I don't track service.. I do that elsewhere. You can set reminders that are triggered by date or odometer. Fuel-up tracks fuel octane, cost, cost per gallon, service station location and brand, receipts, pictures, payment type, city vs high way and whether it was a full or partial fuel-up

 

[DuckNut]

Yes.. it's an app. Fuelly

I've been tracking all my vehicles for years.

You can log Fuel-up & Service, make Notes that include the odometer reading, date, details include tags, add pictures, location and payment type. Same details for Service with the addition of adding receipts, merchant info, and unlimited services you can choose from a list or free text. I don't track service.. I do that elsewhere. You can set reminders that are triggered by date or odometer. Fuel-up tracks fuel octane, cost, cost per gallon, service station location and brand, receipts, pictures, payment type, city vs high way and whether it was a full or partial fuel-up

View attachment 547741

View attachment 547750

View attachment 547742

View attachment 547746


View attachment 547743

View attachment 547747

View attachment 547748

Love it. Thank you.

 

[tr21triton]

Something has to be wrong. MY 2006 Rubicon (not an LJ) with a 4" lift, stock 4.10 gears and very heavy LT285/70R16 tires has averaged 16.16 mpg over the past 30,000 miles.

wow glad somebody else is getting this ! my last 2 tanks have been 17 and 16mpg. before adding 10% for larger tire offset ! was thinking I might be rebuilding the engine soon, figured it might be like a light bulb, shines brightest right before burning out I was getting consistent 15 before replacing my Cadillac converters

 

[ItchyDong]

My guess would be old, tired, lazy upstream O2 sensors. I'm not saying it would fix it entirely, but if I had a gun to my head and no live data to look at, that'd be the first thing I replaced. The threshold for a "slow response" DTC on these old girls is virtually non-existent. More commonly, you'll never see a check engine light for an 02 until the heater circuit goes out, which, has nothing to do with MPG.

Long Term Fuel trims would be a really valuable thing to look at right now.

 

[Vtx531]

It should throw a code if using more than 20%? fuel from the factory maps for given load. You are almost 100% more fuel. It would run like total garbage if it was actually using that much fuel. Even if you didn't change the speedometer for tires (maybe I missed that) it wouldn't account for that much difference. Lots of idling? Dragging brakes? Somebody syphoning your gas out?? Gas station pump meter rigged?

 

[DuckNut]

Stick your finger in the tailpipe, if it doesn't feel like thick black fuzzy socks, I agree with @Vtx531

 

[TurboTJ]

My 2006 Rubicon with 32s only gets about 10 mpg around town. Oh yeah, there is the turbo, and my right foot just can’t help itself . On the road I get more like 14 mpg.

 

[Just Chillin]

So, if you start with your vehicle stock, it came with 30 9.5R15 tires that actually measure just less than 29in mounted as a spare. You have Increased the tire size by at least 3 inches. You also lifted the vehicle and created more wind resistance. Add in some miles on the motor, maybe old plugs, a dirty MAF sensor, dirty throttle body, old plugs and you might be getting close to your numbers.

I have an 05 with the same axles. I have 31in tires. 95% of my trips to the store, Home Depot or In N Out burger are less than a mile. I am sure I get just as lousy mileage as you. I live at the top of a hill. So I am hauling that Jeep up the hill on the way home every time.

I have 4.56s in the garage waiting for me to install them. Most of the responses above (with better mileage) have lower gears than you.