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Old 06-14-2014, 03:01 PM   #1
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Fuel Consumption

Since I am still very new to Jeeps I was wondering if anyone could tell me how many miles your YJ gets on a tank. Mine is an '89 4-cyl and I believe I'm roughly getting 160 miles on a 15 gallon tank. I figured it should be more. Also I'm not getting much power if any out of 5th gear. At what RPMs do y'all shift? Any help would be appreciated .

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Old 06-14-2014, 04:30 PM   #2
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I have a 90 YJ 2.5 TBI 5 speed with 4.10 gears with 2357515 tires soft top and soft doors. I get 165 out of 3/4 of a tank... I always fill up on 1/4 tank. If I push it I could get 200 out of 15 gallons.. Gotta love the flying Brick. If I wind it up good I can cruise 75 on the freeway but dont do that very often.. My RPM's are 3000k at 65 miles per hour in 5th gear. My average mileage is 14.5/15 MPG city and highway about equal.

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Old 06-14-2014, 04:44 PM   #3
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Thanks, yea that's part of my issue. 31x10.50 tires and a broken fuel gauge. So it doesn't seem like I'm to far off. Still does anyone have any suggestions why when I shift to 5th I lose a ton of speed, rpms, and power
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Old 06-14-2014, 07:45 PM   #4
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Thanks, yea that's part of my issue. 31x10.50 tires and a broken fuel gauge. So it doesn't seem like I'm to far off. Still does anyone have any suggestions why when I shift to 5th I lose a ton of speed, rpms, and power

Did not know your running 31's you need a regear 4.56 or 4.88. or go back to stock tires.
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Old 06-14-2014, 10:45 PM   #5
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Had no clue, could this be part of the issue you think?
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Old 06-14-2014, 10:51 PM   #6
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Remember I'm brand new at this so please break it down for me.
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Old 06-15-2014, 08:05 AM   #7
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Well the gear ratio changes with the larger the tire size... Bigger tires higher gear ratio... The little 2.5 does not have enough power to turn the larger tires with a higher gear ratio in 5th gear. Thats why your in 4th gear all the time... Your only solution is go smaller tires (stock) Im running 2 sizes larger almost 29" 2357515 and no problem in 5th gear.. Stock size tires are 27" When going to a front axle and rear axle lower gear (4.56/4.88) you are returning the gear ratio almost to stock in account for the larger tires you are running inturn the little 2.5 is now within its gear and power band. You can pretend you have a 4 speed and forget about 5 gear or go with a axle gear change which involves front and rear axles... kinda pricy or return to stock size tires. Hope this helps...
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Old 06-15-2014, 08:28 AM   #8
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Remember I'm brand new at this so please break it down for me.
These flying bricks are so cool to drive down the road... They are a animal all to themselves. There is so much to these vehicles and so much you can do with them.... I would suggest going to the YJ build section read all the things other people have done to there vehicles... Also get you a factory service manual. So you can fix your gas gauge.. There is a ton of information that have already been done what your fixing to start doing to your Jeep... Its a great adventure working on your new Jeep as well as the adventures you go on where no FORD FOCUS will ever go. ...

and
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Old 06-15-2014, 02:55 PM   #9
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So what is the largest "safe" size tire for a 4.2 with stock front and rear?
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Old 06-15-2014, 05:02 PM   #10
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jumping in here with a question that MAY help...what gears did the 5 speed 4 cyl come with? I hear the auto's had 4.10's. there's a pair of 4.10 axles on craigslist here for $150, cheaper than a gear change. or is that not enough of a change to be worth the trouble?
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Old 06-15-2014, 05:10 PM   #11
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jumping in here with a question that MAY help...what gears did the 5 speed 4 cyl come with? I hear the auto's had 4.10's. there's a pair of 4.10 axles on craigslist here for $150, cheaper than a gear change. or is that not enough of a change to be worth the trouble?
My 4 squirrels came with 4.10's and im 5 speed.
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Old 06-15-2014, 05:15 PM   #12
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So what is the largest "safe" size tire for a 4.2 with stock front and rear?
From my understanding from reading this forum 6cyl Jeeps can run 33's on stock gears (safe would be 31's). Hopefully a Jeep guru will jump in.... I can tell ya all about 4cyl's but know little about 6cyl's. The only thing about a 6cyl I can tell ya is I wish my jeep had one.
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Old 06-15-2014, 05:26 PM   #13
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So what is the largest "safe" size tire for a 4.2 with stock front and rear?
First off, what is your jeep sitting at, is it stock or does it have a lift?
If its stock then you won't be able to get anything bigger than a 31 under there and thats probably even pushing it. as far as your axles go if you have the stock d30 and d35 theres no point in trying to run anything bigger than a 33. Its not a question of if your axles will break but when they will.
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Old 06-16-2014, 12:33 PM   #14
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It only has a 1 inch body lift, all else is stock. I dont really want bigger then 31s at this point.

would I be better off putting on spacers as well?
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Old 06-16-2014, 01:21 PM   #15
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Not sure on the spacers, but You should be fine running 31s
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Old 06-16-2014, 01:23 PM   #16
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It only has a 1 inch body lift, all else is stock. I dont really want bigger then 31s at this point.

would I be better off putting on spacers as well?
If your going 31's I would go with these

Boomerang Lift Shackles for Jeep YJ Wrangler (Front / Rear), CJ (Rear) [RC0401] | Rough Country Suspension Systems

These will give you a little room to breathe with 31's and wont break the bank, If I go to 31's and these N78-15 6 PLY BUCKSHOT MUDDER BLK TL - New Products I will definately go with these Boomerang Lift Shackles for Jeep YJ Wrangler (Front / Rear), CJ (Rear) [RC0401] | Rough Country Suspension Systems

My factory springs still have a great arch....
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Old 06-16-2014, 01:25 PM   #17
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Thanks very much. I guess that will be the next purchase.

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