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Old 04-20-2008, 12:22 AM   #1
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whats up with my gas mileage

just so you know I am very meticulous on keeping my vehicles tuned up

as of the last couple of weeks I have been getting 10 miles per gallon in town
and about 8 miles per gallon hwy
but today I went up the mt which is basically a 2wd dirt road and after 50 miles I had 1/2 a tank
it seams like every time I go off road I use allot of gas
A few weeks ago I did this trail that was about 2 miles long but takes you like 4 hours to travel it
and it took me 3/4 of a tank of gas


I think I need to sell my jeep and buy a grand cherokee with the V8 I should get better gas mileage then I'm getting now

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Old 04-20-2008, 01:53 AM   #2
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Probably, I'm getting better mileage in my Grand than Amy does in her Wrangler and I've actually got power again.

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Old 04-20-2008, 02:42 AM   #3
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Old 04-20-2008, 08:42 AM   #4
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Do you have the correct speedo gear installed? I get about 13-14 highway with 35's and 4.56.
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Old 04-20-2008, 08:51 AM   #5
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how may miles on her? Ever replace the upstream o2?
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Old 04-20-2008, 11:12 AM   #6
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Quote:
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Do you have the correct speedo gear installed? I get about 13-14 highway with 35's and 4.56.
yep the correct speedo gear was installed right after I put the 35's on

Quote:
Originally Posted by 4.0l sahara View Post
how may miles on her? Ever replace the upstream o2?
yep all the 02 sensors have been replaced
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Old 04-20-2008, 11:19 AM   #7
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what gear is that? 29 tooth?

As for city hw driving.. What psi are your tires as of right now (not what you put in there a month ago)?
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Old 04-20-2008, 04:55 PM   #8
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what gear is that? 29 tooth?

As for city hw driving.. What psi are your tires as of right now (not what you put in there a month ago)?
I'm running a 37 tooth speedo gear and according to the GPS I am right on
I change that so my odometer reads correctly other wise I would be reading twice the amount of miles on it then there really are


right know my tires have 8 psi but I go wheeling on the weekends
and I havent aired my tires up yet I wheeled all day yesterday and today I went out this morning I just got back about an hour ago and I will probably go back out in about an hour
but for day to day during the work week I run 30psi in the tires
why air them back up if I'm going out again (well I will air them up if I have alot of driving to get home or to the trail)
but out here I can hit the trails within 5 min. from my house
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Old 04-20-2008, 05:03 PM   #9
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nvm on the 29 tooth gear, didnt see you had 4.56 gears.
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Old 04-20-2008, 05:05 PM   #10
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Sheesh, air up before you head home man. Tires can overheat and fail when they're so underinflated and you drive much faster than 20-25 mph on your trips between the trail and home. Were your tires aired down when you noted the poor mileage?
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Old 04-20-2008, 05:57 PM   #11
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Sheesh, air up before you head home man. Tires can overheat and fail when they're so underinflated and you drive much faster than 20-25 mph on your trips between the trail and home. Were your tires aired down when you noted the poor mileage?
nope that's every day I have always gotten worse mileage on the hwy then in town

it takes me 5 min. to get home from the desert it takes longer to air up

this morning it took me longer to get home but its only becaus I stoped at the tire stoe to get a spare so I had a replacement
incase I pop another last night a stick jumped out and whent through my sidewall so I replaced it with a spar and this morning a rock whent though a diffrent side wall
( I really need to buy some tsl's) maybe I wont go through tires as much
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Old 04-20-2008, 06:05 PM   #12
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how's the state of tune? cap rotor plugs wires fuel filter?

never mind, didn't read the first line.
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Old 04-20-2008, 06:50 PM   #13
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There are lots of things that can cause this.

Any vac leaks?
check the timing with a scanner or laptop.
something is probably causing a rich condition. Any codes? Dirty air filter? Is the engine reaching operating temp?
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Old 04-20-2008, 09:22 PM   #14
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There are lots of things that can cause this.

Any vac leaks?
check the timing with a scanner or laptop.
something is probably causing a rich condition. Any codes? Dirty air filter? Is the engine reaching operating temp?

no vac leaks
timing is computer controlled so I will have to take it to a friend of mine and have him hook up the scanner
as far as operating temp it stays right under the 210 mark and right on the 210 mark with the ac running
I'm running the 2speed electric taurus fan
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Old 04-20-2008, 09:37 PM   #15
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30 psi is a bit low for everyday driving, and with that size tire, tire pressure will have a more pronounced effect on gas mileage. The wrangler only weighing 3000 lbs or so, the tire pressure should be around 32. I run at 35 and haven't noticed any negative affects on the tires, and the gas mileage jumped a lot. They were at 28ish after I bought it and it was a few days before I was able to get back home from school to use the air compressor.

Cat?...collapsed muffler? Dirty throttle body? Gas mileage is a tricky bastard. Just keep checking the little things and you'll figure it out.
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Old 04-20-2008, 10:22 PM   #16
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Gas mileage is a tricky bastard.
haha a brick and mpg dont like eachother.
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Old 04-20-2008, 11:06 PM   #17
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30 psi is a bit low for everyday driving, and with that size tire, tire pressure will have a more pronounced effect on gas mileage. The wrangler only weighing 3000 lbs or so, the tire pressure should be around 32. I run at 35 and haven't noticed any negative affects on the tires, and the gas mileage jumped a lot. They were at 28ish after I bought it and it was a few days before I was able to get back home from school to use the air compressor.

Cat?...collapsed muffler? Dirty throttle body? Gas mileage is a tricky bastard. Just keep checking the little things and you'll figure it out.
new high flow cat newer high flow muffler clean throttle body

and 30 psi on a light wrangler with a tire that has a heavier side wall then the street tires that come on a jeep from factory
is quite high from what everyone else says

now remember you gas mileage suffers a little with a mud tire

with the wrangler I don't expect to get anything better then my F250 with the 460 in it

but why does my gas mileage drop so drastically when I hit the dirt
my rpm's stay low there isn't much of a strain on the engine
and since I'm running a full electric 2 speed taurus fan it not only gave me more power but it took the drag off the motor



its kinda sad that my f250 with the 460 motor in it gets the same mpg as the tj
which is worse then my dads H2 gets he gets 13 mpg in that
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Old 04-20-2008, 11:08 PM   #18
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yeah that does get me thinking why the wrangler motors are so inefficient.
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Old 04-20-2008, 11:10 PM   #19
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yeah that does get me thinking why the wrangler motors are so inefficient.
I have kinda wondered that myself
its only 6 cylinders and you dont even have that much horse power
I wonder if I put an ls1 in if my gas milage would go up
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Old 04-20-2008, 11:24 PM   #20
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Your mpg dropping when wheeling is normal. On the hwy it should be better though. I just averaged 17mpg on the hwy the other day, but I have 3:73's and 33's. You have to consider tire size and gears which you already know, is going to effect your mileage. Your driving style will also, like driving on deflated tires or heavy footing the throttle. It sounds like there is something more than the usual mpg problems giving you trouble, but the LS1 could cure that.
BTW hows that new muffler sound?
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Old 04-21-2008, 12:30 AM   #21
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I agree with 4point, I have the same stats as him as far as gears tires and MPGs. I wheeled hard a few weekends ago for 2 days averaging 45 to 50mph with lots of wheel spin and i still eaked out 13mpg on my way to the the meeting spot for the run i did 3hours on the highway and averaged 17mpg.

I have synthetic in the axles, and trans. castrol 10w30 in the motor. electric fan, flowmaster exhaust. I use the champion copper truck plugs.I also sea foam my motor regularly. the only time i had bad fuel mileage like with what your talking about is when I was playing with the motor and unplugged the factory coolant temp sender. I did like 40 miles on a half tank. i plugged it back in and everything went back to normal. check your plugs make sure there not covered in carbon. check your plug gaps. do you have a stick or auto??? if you have an auto when was the last time you serviced the trans? a dirty trans filter and old fluid will mess with shifts and MPGs too. dont forget to make sure your air filer is clean. Im running the true flow drop in filter and it works great.
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Old 04-21-2008, 01:32 AM   #22
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BTW hows that new muffler sound?
it sounds good


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auto when was the last time you serviced the trans? a dirty trans filter and old fluid will mess with shifts and MPGs too. dont forget to make sure your air filer is clean. Im running the true flow drop in filter and it works great.
I didnt think of the trans
the only reason I can think of why my gas milage sucks on the hwy is the three speed auto trans
2900 rpm at 60 and 3250 rpm at 70 I would think the hwy gas milage would suffer

but I have never been able to get 17 mpg out of my jeep
when I bought it it had a 3" lift 33's and 3.07 gears
I would get about 120-130 per full tank of gas
now I get around 180-200 per tank of gas

right now a friend just dropped off his jeep so I could fix his oil pan install an electric fan and put in his new gen right crawler tank
and in return he is giving me some new never used rock sliders
so I'll have to wait on my jeep for a few days

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Old 04-21-2008, 06:44 AM   #23
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I just averaged 17mpg on the hwy the other day, but I have 3:73's and 33's.

I wish.
That's my setup but I'm only getting about 195 out of a tank. My mpg is suffering too. I'm thinking cat or o2 but not sure how to diagnose the cat.
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Old 04-21-2008, 09:51 AM   #24
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if you end up servicing the trans make sure you put atf +4 or synthetic in the 3 speed
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Old 04-21-2008, 11:53 AM   #25
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if you end up servicing the trans make sure you put atf +4 or synthetic in the 3 speed
I was thinking of using royal purple its synthetic
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Old 04-21-2008, 11:59 AM   #26
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Aren't all ATF+4s synthetic? I used Valvoline ATF+4 to refill my new 3-speed auto, it's hard to beat.
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Old 04-21-2008, 12:38 PM   #27
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I wish.
That's my setup but I'm only getting about 195 out of a tank. My mpg is suffering too. I'm thinking cat or o2 but not sure how to diagnose the cat.

Knock on it. If it rattles its falling apart, not necessarily catastrophic to gas mileage but time for a new one none the less. A cat that's catalyst has been "poisoned" will cause the exhaust to smell like rotten eggs and typically trip a catalytic converter inefficiency code.

The stock cats suck, so not a bad place to start.

300 miles per tank without a good tune. The 2.5s not all bad
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Old 04-21-2008, 08:13 PM   #28
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well I was thinking that I'm going to change out my idle control sensor since its been giving me a rough idle in the mornings or when the motor is cold
and replace the 02 sensors even though I replaced them about 15,000 miles ago
I have notice the last couple of weeks that I'm getting about 130-150 miles to a tank of gas

so once I have a little bit of money I will replace those sensors and let you know if that works

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