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

[deadbeat son]

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.

A year ago, I bought an 05 with 37k miles, 3.73 gears, auto, and 30x9.5 mild AT tires. Right after buying it, I drove it from CO to KS to visit family, 760 miles round trip. I don’t recall exact fuel mileage from that trip, but when I calculated it I was astounded that it was > 20mpg.

Even with a change from 30s to 32s, I would expect to see much better than 8.4 mpg if running properly.

 

[buildbigboats]

Thanks everyone for the input.
Have yet to hook up OBD reader to see live data.
I recently purchased at new Flowmaster catalytic converter setup based on heads-up thread a few weeks ago. Thought I'd keep it for just in case if needed but maybe it's time to replace them. Also have a full set of NGK O2 sensors also in the spares bin that I'll install along with the new cats. Other than the transmission/torque converter possible issue mentioned not sure what else could be left. After doing that if still crappy may have to take it to local shop for deep dive diagnostics.

 

[NskLJ]

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

I would start by calibrating the speedometer/odometer. You have about a 14% tire size difference. How are you calculating fuel mileage? ( this may sound dumb but it’s relevant)
https://www.tacomaworld.com/tirecalc?tires=205-75r15-265-70r17

 

[deadbeat son]

I would start by calibrating the speedometer/odometer. You have about a 14% tire size difference. How are you calculating fuel mileage? ( this may sound dumb but it’s relevant)
https://www.tacomaworld.com/tirecalc?tires=205-75r15-265-70r17

This is a great point, but his stock tire size was probably 30x9.50r15, which is only a 5% difference in revolutions per mile. I don't believe the LJ was ever available with a 205/75r15; only 30x9.5r15 for non Rubicon and 245/75r16 for Rubicon models..