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Rolling Mod
04 Wrangler Unlimited, 67 F100
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41,536 Posts
Discussion Starter #1 (Edited)
So we drove my stockish Jeep LJ up the coast this weekend. Stock with 2” spacer lift and 31’s. I wasn’t able to get exact mileage due to a screwey gas pump, but the Jeep is getting less than 10 mpg. To me this seems excessively low.

No cel on, engine runs smooth and does not sputter, tailpipe does not spell like fuel and the Jeep does not smoke. Easily passed smog this year.

What should I look at first? Jeep has 200,000+ miles and I have not yet done a tuneup or o2 sensor. What else should I look at?
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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41,536 Posts
Discussion Starter #4
Are you sure the odometer is reading the correct mileage?
The odometer I used was in my Sienna. We filled both up and drove. The Sienna went 176 miles on about 7.8 gallons. The Jeep burned to E and the same 7.8 gallons gave just at 1/2 tank. (Pre pay gas station with huge lines. $30/ea car). I slightly concerned that the float might be munched, but it hasn’t seemed to be an issue running around LA.

Speed was 70-80mph depending on traffic.
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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41,536 Posts
Discussion Starter #5
i never get more than 200 miles on 1 full tank - 4.0 HO 1994 YJ

i had 3 different jeeps 4.0 and never got good millage
im running AW4 tranny

id do tune up, fuel filter,and check cat maybe?
My old TJ did 10 mpg. 4.0 5spd 6.5” lift and 35’s or 37’s. Was thinking this would do better dud to being lower. When I lowered the white Jeep it did better. Taller was bad.
 

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The odometer I used was in my Sienna. We filled both up and drove. The Sienna went 176 miles on about 7.8 gallons. The Jeep burned to E and the same 7.8 gallons gave just at 1/2 tank. (Pre pay gas station with huge lines. $30/ea car). I slightly concerned that the float might be munched, but it hasn’t seemed to be an issue running around LA.

Speed was 70-80mph depending on traffic.
How many gallons did you use to fill the LJ back up?
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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Discussion Starter #7
How many gallons did you use to fill the LJ back up?
We drove another 90 miles, and I don’t know. Caregiver did it and I can’t find receipt. To be truthful I was running late stop to stop and I was stressing about other stuff too. If I was in the Jeep, I always calculate. I just was distracted otherwise I would have exact numbers.
 

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We drove another 90 miles, and I don’t know. Caregiver did it and I can’t find receipt. To be truthful I was running late stop to stop and I was stressing about other stuff too. If I was in the Jeep, I always calculate. I just was distracted otherwise I would have exact numbers.
Doesn't know true MPG. Asks questions about MPG anyways. :flipoff2:



Regardless, everything sounds normal to me.
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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Discussion Starter #9
Doesn't know true MPG. Asks questions about MPG anyways. :flipoff2:



Regardless, everything sounds normal to me.
I know. :homer: It was just much lower than I was hoping for stock. I was hoping for over 10mpg modded. 11 or 12 ish modded. Eh. I care more about range than mpg. I hate stopping on road trips. 100 gal transfer tank in bed? :grinpimp:
 

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"Speed was 70-80mph depending on traffic."

Cut your speed back and your mileage will go dramatically up! 55-62 seems to be the sweet spot, if you can avoid getting run over!
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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41,536 Posts
Discussion Starter #12
"Speed was 70-80mph depending on traffic."

Cut your speed back and your mileage will go dramatically up! 55-62 seems to be the sweet spot, if you can avoid getting run over!
Ain’t nobody got time fo that! :flipoff2:
 

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I just got back from an 1800 mile trip in my 5.2l V8 CJ-8 towing my 1700 lb. teardrop trailer. I went to the Needles district of the Canyonlands NP. among other places along the way. The jeep and trailer run on 33-10.50-15 BFG Mud terrains and 4:10 gears. RPM in 5th is about 1900 at 65 mph.

In Kommiefornia, the speed limit towing a trailer is 55. Usually in CA, I'll keep it down to 58-62 where the cops don't seem to go after you at, mpg will average 12.5-14.5 depending on the terrain. When I hit Arizona, I sped up to the 75 mph limit to cover some terrain to Flagstaff, MPG dropped to 11.5. I slowed down again the next day and with the better non-ethanol gas there, I got about 15.5 mpg. Driving back to get home, I hit 80 in some spots in AZ, Mileage was closer to 10 mpg. 9.5 to 10 mpg is what I get while I was wheeling in it towing the trailer around the Needles district and the various forest routes in the area.
 

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Almost forgot, a buddy has an '04 LJ automatic hardtop, with 3.73's and 33" tires with a 2.5" lift. When we travel together at the slower speeds with me towing, we get about the same MPG's, him slightly better most times. He has to fill up more often though as I have a 33 gallon Aero tank, he has the stock 19 gallon tank.
 

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P.B.A.
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Almost forgot, a buddy has an '04 LJ automatic hardtop, with 3.73's and 33" tires with a 2.5" lift. When we travel together at the slower speeds with me towing, we get about the same MPG's, him slightly better most times. He has to fill up more often though as I have a 33 gallon Aero tank, he has the stock 19 gallon tank.
Any ideas for frank to look at on his rig? Oh master of the 4.0.

And I agree mileage should be better.
 

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Watching intently, but skeptically. I've got an XJ on 31s that consistently gets 10-11, before and after lots of tuneup and maintenance catch-up.
 

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Frank, I'm afraid you're on track with your 10ish mpg, your calcs leave room for it to be 12mpg. and 12 is what I would expect to be the top.

At least compared to my 05.
 

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Fuel injection or ignition causing poor mileage would show up with fault codes.

A partially plugged cat con might not throw a code or cut power too much. A fitting can be made from an old sensor or a compression tester 18mm adapter to allow use of a low pressure fuel pump test gauge through the upstream O2 sensor threaded fittings. Anything over about 2 psi is getting towards the high side, 5 psi would indicate plugging.

https://www.youtube.com/watch?v=xrUjD69kDng

A Federal Emissions spec TJ might only have one big cat, Kommiefornia spec ones have two upstream cats and one larger one ahead of the muffler. The downstream cat and muffler can be checked for restriction by testing for backpressure at the downstream O2 sensor port

My friend with the '04 LJ picked up a mile per gallon when he gutted his plugged upstream cats.

The best method for better fuel mileage is to slow down, as previously mentioned. Jeep is a brick moving down the road, wind resistance rises exponentially with speed. Lifting my jeep 2.5" dropped mileage 1.5 mpg when I still had the 4.2l in it, no other mods at the same time. Has to be attributed to wind resistance.

Mpg For Speed - Fuel Efficiency Vs. Speed
 
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