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Discussion Starter · #1 ·
So for the 1.5 years of glorious ownership I have gone from getting more or less than 16 MPG on the highway and 13-14 city, to a pathetic 9 MPG.

Since modifications like heavier bumpers and a winch I expected my MPG to drop and it did, just 1 MPG. Since about May of 2014, I've noticed a steady decline in MPG. I thought nothing of it thinking it was driving habits. Then in Febuary this year I installed my roof rack. Again, same expectations were a drop in MPG and it did. I didnt really think too much of it, but then I took a highway trip to go wheeling. Going about 70 MPH the entire highway trip I averaged 9 MPG and sometimes even less! HIGHWAY! :puke: I know roof racks cause drag, and if our toaster on wheels wasn't already unaerodynamic enough, but there is no reason I should be averaging 9 MPG. I think there maybe something more wrong than drag currently with my Jeep and I'm hoping yall could help me out. :pullinghair:

My thoughts maybe potentially spark plugs but I'm not remotely sure. I believe they are OEM and are still stock straight from the dealership. Also plan to clean my air filter and also B12 the throttle body. I know Jeeps are no eco automobile, but damn I now miss getting 12 MPG.

Backround info: 2005 Jeep Wrangler Rubicon, 33"x10.5" BFG KOs, 4.10 gears (dont start the regear :censored:, I know I need 4.56 but it still shouldnt be that bad), ARB front/rear bumpers, Warn M8000, Gobi Ranger Roof Rack, AFE hot air intake, Magna Flow exhaust, 45k miles, less than 5000 miles since last oil/oil filter change, brand spanking new catalytic converter, 6-speed NSG-370 Hitler tranny
 

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Obviously the weight is working against you but I'd start with some easy stuff you can tackle yourself like plugs and wires, air filter, tire pressure, routine stuff
 

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I feel your pain. I'm running 33s but I have 3.73 gears. Trying to save up for the 4.56s!
 

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Discussion Starter · #6 ·
Obviously the weight is working against you but I'd start with some easy stuff you can tackle yourself like plugs and wires, air filter, tire pressure, routine stuff
Yeah there is definitely some more weight, but I know people that average better MPG with more weight, just still shouldn't be averaging 9 MPG. Pressure is 28 psi in the front and 26 psi in the rear. Also going to check my PCV valves and make sure nothing is clogged. Also thinking maybe vaccum lines? Also heard that factory plugs for Jeeps in that generation span were pretty POS and were only designed to last 30k miles but I have no idea how true that is
 

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Discussion Starter · #8 ·
There may have been a problem when they were replaced, you can give that a look and see if it's dragging
I did have to have them readjust the calipers when I got it back. I had a soft pedal and also was pulling left when braking. They fixed that but I need to take it back. I get a loud groan sometimes from the rear making me believe the rear calipers might be too tight and again adjusted. It might be partially the problem but still doesn't justify the :censored: fuel economy I was getting before I had them fixed. I was getting about 10 MPG before they were replaced
 

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A bad upstream 02 sensor can fool the ECM into setting the fuel mixture too rich which will wreck the mpg and worsen performance too. They need to be replaced every so often and your TJ is old enough that it may be time.
 

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Discussion Starter · #10 ·
A bad upstream 02 sensor can fool the ECM into setting the fuel mixture too rich which will wreck the mpg and worsen performance too. They need to be replaced every so often and your TJ is old enough that it may be time.
Forgot to mention. Those are brand spanking new too:) I replaced those first when trying to sort out my CEL which turned out to be my catalytic converter
 

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70 MPH might be your problem. Aerodynamic drag is exponential and you have a lot of stuff hanging on that Jeep. Double the speed and increase the drag force 400%. At 70 MPH your drag is 65% higher than at 55MPH. I bet at 55MPH your mileage would be somewhere in the teens.
 

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Discussion Starter · #14 ·
70 MPH might be your problem. Aerodynamic drag is exponential and you have a lot of stuff hanging on that Jeep. Double the speed and increase the drag force 400%. At 70 MPH your drag is 65% higher than at 55MPH. I bet at 55MPH your mileage would be somewhere in the teens.
65-70 MPH is where I used to get my best fuel economy. It's really the only speed that makes my 6th gear useful. 55 MPH is actually that really screwy speed for me where I either need to decide to lug the engine in 5th or stay in high RPMs in 4th
 

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Taco, I would use a laser thermometer on the breaks after a trip. I think with all the "new" break work, it may have introduced a problem. Good luck.
 

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Discussion Starter · #16 ·
Taco, I would use a laser thermometer on the breaks after a trip. I think with all the "new" break work, it may have introduced a problem. Good luck.
Are you saying that there still maybe contact with the pads and discs even after I've gotten up to speed?
 

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Absolutely, I think if they are dragging the condition will exist no matter the speed. If you have a laser thermometer handy it is super easy to check. If not, you can remove the tire and check for drag by turning the brake disk.
 

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Disk brake pads naturally ride on the rotor, they don't ride above it like drum brake shoes do above the drum.
 

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Discussion Starter · #19 ·
Absolutely, I think if they are dragging the condition will exist no matter the speed. If you have a laser thermometer handy it is super easy to check. If not, you can remove the tire and check for drag by turning the brake disk.
Might be. I'm having my mechanic readjust my calipers and pads again next week to fix a groan I sometimes get from the rear brakes. Might help a little but again, it still doesn't explain the horrible fuel eco I was getting before the Jeep went into the shop.
 

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Same diameter, just downsized the width from 33"x12.5". The speedo pinion is off but still doesn't explain a 7 MPG difference
A speedo gear meant for a smaller tire will cause the indicated MPG to be lower than it really is. How much so depends on what size tire the TJ originally came with... some factory size tires are pretty small so there could be a fairly dramatic difference with 33's.

It only takes 5 minutes from start to finish to snap in the correct speedometer gear, I'd do it.
 
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