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Old 10-16-2009, 09:24 PM   #1
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New member, got some ?'s

Hey guys this is my first time on this site so "Hello!". I don't have a Jeep right now, my girlfriend does but is too hardheaded to get in here and ask some questions on a few problems her 06 is having. It's new to us, only two weeks now and has the auto tranny with the 4.0 I6. It's a real dog! No power at all, I know the auto's lose more power than the sticks but hers really is pretty bad. It also only gets about 11 MPG. She works at a Dodge dealership and it's had the full inspection before purchase but I'm sure there's a few things they could've missed. It's all stock except for the Revo tires and they're barely bigger than stock, I have no idea what gears are in it. The thing only has 18,600 miles on it and it in excellent shape, the body, top, and interior are almost perfect and the engine bay looks like it's never needed a cleaning. Any ideas where to start looking for problems? I do have a good bit of mechanic experience so as long as it don't require a computer I can handle most problems. It almost seems to me that the front axle, or transfer case is in 4x4 for some reason even though the shifter is in 2HI and there's no light on anywhere. I had a 94 Wrangler with the 5 speed and 4.0 HO several years ago but this 05 doesn't even compare to the power mine had. I also got close to 20mpg. Any help here is greatly appreciated guys. Thanks in advance!

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Old 10-16-2009, 09:28 PM   #2
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Pull the plugs and check them. I highly doubt it is stuck in 4hi tho. The jeep will not get sluggish in 4hi at all. Do you notice anything like the front brakes sticking?

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Isn't the JK just a rebodied PT Cruiser?!

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Originally Posted by coyote_94yj
Just a few more inches Red. You can take it.


If you haven't gotten more out of the insurance company than you deserve, then you haven't screwed them nearly as much as they have been screwing you for the past xx years.
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Old 10-16-2009, 09:46 PM   #3
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How much bigger are the tires again?

Oh, and go find out what diff/gears she has. On the tag bolted to the diff at 10-11 o'clock position...
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Old 10-16-2009, 09:48 PM   #4
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I am betting she has a 30/35combo and 3.07s.
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Isn't the JK just a rebodied PT Cruiser?!

Quote:
Originally Posted by coyote_94yj
Just a few more inches Red. You can take it.


If you haven't gotten more out of the insurance company than you deserve, then you haven't screwed them nearly as much as they have been screwing you for the past xx years.
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Old 10-16-2009, 09:50 PM   #5
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And probably 31's which will cause the "sluggishness" and give an improper (and lower) MPG reading...
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Old 10-16-2009, 09:58 PM   #6
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I checked the wheels for heat after driving a while and they're normal feeling to me. It tracks straight on the road with no left/right pulling so I don't think it's the brakes. I'll check the gearing in the morning when I can get it on the concrete. I don't remember the exact size on the tires but they're just barely bigger than stock and they're not agressive.
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Old 10-16-2009, 10:01 PM   #7
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Aggressive tires won't have much (if any) effect on MPG or performance of the jeep minus some traction variances.

Post up the tire/wheel size when you check the gearing in the morning too.
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Old 10-16-2009, 10:04 PM   #8
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Ok I checked and they're 31/10.50/15's. That's not enough of an increase to make this big a difference in power and mileage. It's the same size my Jeep had and that little thing had all the power it needed.

P.S. what's the 30/35 combo? Is that the dana axles we're assuming she has?
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Old 10-16-2009, 10:11 PM   #9
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Correct well I know for sure the front is a dana 30. The rear if it has a rubber drain plug it is a dana 35.
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Quote:
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Isn't the JK just a rebodied PT Cruiser?!

Quote:
Originally Posted by coyote_94yj
Just a few more inches Red. You can take it.


If you haven't gotten more out of the insurance company than you deserve, then you haven't screwed them nearly as much as they have been screwing you for the past xx years.
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Old 10-16-2009, 10:21 PM   #10
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I hope this helps so here goes, I also drive the 06 with 4L I-6, when I first got it I thought the same thing, feels like it is stuck in 4 Hi, If you can make a smooth, sharp right turn without the wheel jerking out of your hand, it isn't in 4. They are not fast, but if you need the power for passing, it will amaze you how fast it will get up and go with hard pressure on the accelerator. If you are driving in the city or on the trail, turn off the O/D mode. Use that only for highway. As for mileage, I was getting about the same 11 mpg. When I checked the factory installed plugs, they were gapped to .70, recommended gap is 0.035. I replaced the plugs and now I get about 13 mpg combined city/highway. I also run the 31/10.5/15's. You really can't compare the 06 to your 95. It's never going to have the speed or mileage that you think it should, but it still has the ability to do what a Jeep should do. So love it for what it is and if you come up with something that can help in any of these areas, by all means post it. And BTW Welcome to the Forum.
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Old 10-16-2009, 10:27 PM   #11
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You really can't compare the 06 to your 95. It's never going to have the speed or mileage that you think it should, but it still has the ability to do what a Jeep should do. So love it for what it is and if you come up with something that can help in any of these areas, by all means post it. And BTW Welcome to the Forum.
Really?! I thought these newer Jeeps would be improved in every way over the last ten years. Ok then I'll think differently about it from now on but we'll have to do something about that mileage!
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Old 10-16-2009, 10:37 PM   #12
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Good luck and keep us posted
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Old 10-16-2009, 10:39 PM   #13
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Well, here's the final report on the tire size difference:

60 MPH on stock tires = 53.6 MPH on the new tires.
Speedometer Difference: 11.83% too slow (also the ODO is off this much, i.e the MPG is off about this much).
Diameter Difference: 10.6%

IF you have 3.07 gears, that auto isn't liking it. In addition to the above, the shift points for the tranny is off by that much making a poor situation slightly worse.

Solutions:

A new appropriate sized speedo gear to get the shift points back.

Some 3.73 or 4.11 gears.

If you have or can borrow a GPS, you can verify the above AND calculate the actual MPG too.
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Old 10-16-2009, 10:46 PM   #14
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Not to contradict your research, but I had no loss of MPG's when I changed my stock 30/9.5/15's to the 31/10.5/15's.
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Old 10-16-2009, 10:53 PM   #15
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Thanks for all the replies guys, glad to see I picked a freindly forum! Next question is: power adders. Are they worth it? I'm a deisel guy so I'm not up to date on gas engines but we're looking at cold air intakes, exhaust, and throttle bodies; just light stuff like that. Any suggestions on what to do, what to avoid, what's a waste of money, and what's a 'gotta have'?
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Old 10-16-2009, 10:57 PM   #16
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Not to contradict your research, but I had no loss of MPG's when I changed my stock 30/9.5/15's to the 31/10.5/15's.
That's because you had 30" tires and went to 31" tires. He had P215/75R15's stock and went to 31" tires (where the calculation came from).

And you did have a loss of MPG. Just not big enough for you to notice
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Old 10-19-2009, 08:41 PM   #17
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Ok I've been working on this thing all weekend and found nothing wrong. She put her vin # in the computer and found that her Jeep does have the 30/35 Dana's, tru trac limited slip rear diff., and 3.73's. I can't believe the lack of power in this thing if it has 3.73's, I didn't even know you could get a Wrangler with 3.73's. We did discover that on tight turns on asphalt the front end will chirp, don't know what that's all about. We did put a K&N filter in to hopefully help with the mileage a little. Anybody have experience with power adders for these motors?
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Old 10-19-2009, 08:43 PM   #18
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The best way to add some power is re-gearing the axles.
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Old 10-19-2009, 09:59 PM   #19
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I would put the Jeep on jackstands and put it in drive,see what turns,lol.The front tires chirping?Maybe someone installed a locker in the front.Best way to find out is investigating.I thought my 98 was bad on gas at 16-18 MPG's,I run 29" tires 3.07's with a 4.0 5speed
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Old 10-20-2009, 08:52 PM   #20
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I would put the Jeep on jackstands and put it in drive,see what turns,lol.The front tires chirping?Maybe someone installed a locker in the front.Best way to find out is investigating.I thought my 98 was bad on gas at 16-18 MPG's,I run 29" tires 3.07's with a 4.0 5speed
I haven't had the chance to get all fours on stands yet but I did get the rears up and both tires turn at the same time unless you hold one really hard then you can turn the other but they don't like it. I'd be pretty happy with 16-18 from this one but it's pretty bad when my #8000 diesel gets 16-18 and her Wrangler only gets 11, or 13.8 according what Stevens243 said.
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Old 10-20-2009, 09:34 PM   #21
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You have to remember the diesel has a little curve to the front end. The jeep is a brick. Try this grab a ball throw it then grab a brick see which one flies better.

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Quote:
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Isn't the JK just a rebodied PT Cruiser?!

Quote:
Originally Posted by coyote_94yj
Just a few more inches Red. You can take it.


If you haven't gotten more out of the insurance company than you deserve, then you haven't screwed them nearly as much as they have been screwing you for the past xx years.
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