HORRIBLE MPG Help - Page 2 - JeepForum.com

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post #16 of 42 Old 02-03-2012, 05:24 PM
vanek11
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Quote:
There's also a speedo swap thread on here, you might be able to get one for free.
Please elaborate on the FREE part, mine is off and would like to get it back on track. Thanks

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post #17 of 42 Old 02-03-2012, 05:50 PM
06philaTJ
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Quote:
Originally Posted by Doubblea View Post
First off I would like to thank everyone for the replies. I have 3.07 gears, and the 5 speed ax15. I cleaned the air filter out a month ago when I bought the jeep. I do not know if they are the factory plugs or wires, anyone know what to look for on that?
What rpms are you shifting at? The first reply mentioned one thing that was very common for having bad gas mileage which is lugging your engine. I have 3.07's, 6 speed, no lift, and 235/75/15 A/T tires and it lugs at times if I sink below 2000 rpms especially in 4th gear or higher. I can't use 6th gear unless I'm doing 68-70mph because it lugs the engine and kills my gas mileage.

I've actually calculated my gas mileage several times slightly lugging the engine on my work commutte (city/suburban, no highway, 30-45mph roads) vs. driving aggressive. 12.8-13.94 mpg lugging the engine vs. 16.1-17.71 mpg driving slightly aggressive on the same commutte with the same traffic/weather conditions.

Try shifting above 2500 rpms and cruising at or slightly above 2500 rpms. You may get slightly better gas mileage until you can ditch the 3.07's for a real set of gears/axles.
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post #18 of 42 Old 02-03-2012, 06:09 PM
JBTJ
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Quote:
Originally Posted by vanek11 View Post
Please elaborate on the FREE part, mine is off and would like to get it back on track. Thanks
There is a thread here on this forum where a guy has a deal where you swap out different speed o gears with other people here. You basically let everyone know what gear you have and what gear you need and then find someone to swap gears with. Or you will find someone who has the gear you need. It's worked for lots of people.
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post #19 of 42 Old 02-03-2012, 06:25 PM
Tblack
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You need to add 10 percent to your trip meter when doing your fuel mileage,....( 30" stock tires to 33" tires = +10%) You also shouldnt expect good mileage with 3.07 and 33's. I have 3.73's and i get around 13-14. Ill bet if you geared down to 4.11's and did a speedo gear, your mileage would perk up some. Do a tune up, and ill bet you would get fine mileage. Its a gears game, but its a losing battle against drag. Youll never win, but you can soften the blow. good luck bro!

Safety 3rd!
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post #20 of 42 Old 02-03-2012, 06:53 PM
LJameson
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33's with 3.07...yeah 10 mpg sounds right.

You need to regear to 4.56's and put the right speedo gear in your transfercase. Then you MIGHT see 15 mpg.

1990 YJ-The wheeler
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post #21 of 42 Old 02-03-2012, 06:58 PM
JPNinPA
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Correct the speedo
Plugs, wires cap and rotor
Clean or replace your air filter
Clean the IAC and TB
Check for vac leaks
Other than these cheaper items you could have an issue with the O2 sensors or the CAT.

"Never look down on anyone unless your helping them up"- Jesse Jackson
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post #22 of 42 Old 02-03-2012, 09:01 PM
DevilDogDoc
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Quote:
Originally Posted by LJameson View Post
33's with 3.07...yeah 10 mpg sounds right.

You need to regear to 4.56's and put the right speedo gear in your transfercase. Then you MIGHT see 15 mpg.
I see 15 mpg already......230 to the tank plus correct for 12% difference in the speedo so 250-260 miles to a 15 gallon or so fill 33's on 3.07s......

An ugly Jeep with some stuff.
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post #23 of 42 Old 02-03-2012, 10:20 PM
1999TJRED85000
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4" lift, 33x11x17, 4.56 gearing .... 11.8 mpg.

F U
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post #24 of 42 Old 02-04-2012, 09:13 AM
dscabra
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Quote:
Originally Posted by vanek11 View Post
Important...Check to make sure the speedo is correct. I thought the same also but then realized my speedo is about 10% off. I have a 4" lift and 33" tires also. Just calculated roughly yesterday and found to be getting 14mpg in 75% city driving. When I am going 50 I am actually going 55, so assuming that the odometer is also going to be off, meaning if I travel 50 miles I am actually going 55 miles. Someone correct me if I am wrong but if the speedo is off it would be common sense to me that the odometer would also be off. I am happy at 14mpg with the lift and tires and not driving easy.
Exactly! I put 37's on my F-250 and the spedo was off by 10 mph at 55. My mileage dropped from 16 to 13 mpg based on the truck's computer. I reporogrammed the computer for the correct tire size and my mileage went back up to 15 mpg which means I really only lost about 1 mpg going to the bigger tires -- not the 3 mpg that the computer made it look like.
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post #25 of 42 Old 02-04-2012, 09:21 AM
vanek11
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Quote:
Originally Posted by dscabra View Post
Exactly! I put 37's on my F-250 and the spedo was off by 10 mph at 55. My mileage dropped from 16 to 13 mpg based on the truck's computer. I reporogrammed the computer for the correct tire size and my mileage went back up to 15 mpg which means I really only lost about 1 mpg going to the bigger tires -- not the 3 mpg that the computer made it look like.
See, like I said everything can be deceiving. I would never start a thread on here unless I was getting like 8mpg. Realistically 10-16 mpg is average depending on your set up, driving habits and how far the speedo may be off. Mine is only off like 10% so it isn't a huge deal to me at the moment.
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post #26 of 42 Old 02-04-2012, 10:35 AM
kelso1337
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x2432342 regearing.

It was my problem running 33's on 3.07 gear ratio with the nv3550.
Was getting about 8-12mpg


Now I get 15-20

Stock 2003 Jeep TJ - 'Intense Blue'
Bought the jeep in April, found JF in May...
First Mod in June.
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post #27 of 42 Old 02-05-2012, 10:03 PM Thread Starter
Doubblea
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Well i did the tune up and it gained .5 mpg.. After reading i believe im lugging the engine, as i go 55 at 1800 rpms. My spedo is not correct but i use my phone to know my correct speed, as well as the miles, so there isnt a problem there. I do realize i need to regear, and plan to go to 4.11, but im only 17, and have been looking everywhere for a job, so until that happens i wont have the funds to do it. Any other suggestions are appreciated.
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post #28 of 42 Old 02-05-2012, 11:26 PM
JPNinPA
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1/2 mpg is a 3-5% improvement. Not bad. What does not lugging and keeping it at or above 2200 rpm's?

"Never look down on anyone unless your helping them up"- Jesse Jackson
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post #29 of 42 Old 02-06-2012, 07:35 AM
djflyy
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Quote:
Originally Posted by Doubblea View Post
Well i did the tune up and it gained .5 mpg.. After reading i believe im lugging the engine, as i go 55 at 1800 rpms. My spedo is not correct but i use my phone to know my correct speed, as well as the miles, so there isnt a problem there. I do realize i need to regear, and plan to go to 4.11, but im only 17, and have been looking everywhere for a job, so until that happens i wont have the funds to do it. Any other suggestions are appreciated.
Search junk yards and craigslist for the axles from a 97-06 SE (4 cyl) Wrangler with 4.10 gearing. www.car-part.com will help. The pair can be picked up for $200 if you search well enough. And most of the time, someone will buy your D30/35 combo as well.
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post #30 of 42 Old 02-06-2012, 12:31 PM
rocketgirlCO
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I had the same problem before my CAT went out.. 10MPG was the "most" I'd get.. Your CAT might be close to going if it's older.. Just a thought.
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