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Old 01-26-2014, 08:29 AM   #1
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Before you say "why did you get a jeep" I now the mileage isn't suppose to be good but I'm getting 14 mpg with a stock Sahara. I have 30" 3.73 gears and the 3 speed auto. The 14 is a combination of city and highway but mostly highway. I drive it like a granny so is there anything I can do to get more mpg?

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Old 01-26-2014, 08:49 AM   #2
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How are you calculating your MPG?

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Old 01-26-2014, 08:56 AM   #3
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Setting trip when I fill up drive then fill up again take the miles traveled divided by the gallons.

Wait I just realized this while reading another thread. My speedo is off it says that I'm going 5 mph faster than I am going. Would this throw off my trip.
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Old 01-26-2014, 08:58 AM   #4
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Setting trip when I fill up drive then fill up again take the miles traveled divided by the gallons.

Wait I just realized this while reading another thread. My speedo is off it says that I'm going 5 mph faster than I am going. Would this throw off my trip.
I do believe it would throw off your trip
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Old 01-26-2014, 08:59 AM   #5
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Would it say I traveled more or less miles that I actually did
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Old 01-26-2014, 09:07 AM   #6
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Regarding helping traction with open Diffy look here

parking brake and open differentials and more torque to tires with traction.

As for gas mileage
1) what is your gear ratio in Diffy
2) what tire pressure are you running
3) 2003 was the year they changed to automatic tranny with overdrive
a) is you tranny shifting into OD at highway speed
b) have you made sure the center pod switch is not set to keep tranny out of OD
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Old 01-26-2014, 09:09 AM   #7
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Sorry posted in wrong thread
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Old 01-26-2014, 09:18 AM   #8
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Would it say I traveled more or less miles that I actually did
should show more miles than you actually did since its showing your going 5 mph faster than you are
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Old 01-26-2014, 09:19 AM   #9
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So it's saying I'm getting better mpg then what I actually am
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Old 01-26-2014, 09:26 AM   #10
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So it's saying I'm getting better mpg then what I actually am
I believe so I'm trying to figure it all in my head I'm thinking that it should be better than what your getting
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Old 01-26-2014, 09:29 AM   #11
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If your speed and distance are reading lower than actual because of bigger tires and you use odometer for distance in MPG calc yes you are doing better than calculated because you went further then indicated on the gas you used
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Old 01-26-2014, 09:33 AM   #12
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If your speed and distance are reading lower than actual because of bigger tires and you use odometer for distance in MPG calc yes you are doing better than calculated because you went further then indicated on the gas you used
My tires are stock 30". But my speedo says I'm going faster than I am
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Old 01-26-2014, 09:49 AM   #13
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My tires are stock 30". But my speedo says I'm going faster than I am
Though your tires are stock if its still reading faster than your going it should still make the trip meter read more than you went so you should still be getting better than you figured
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Old 01-26-2014, 09:51 AM   #14
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Though your tires are stock if its still reading faster than your going it should still make the trip meter read more than you went so you should still be getting better than you figured
So instead of 14 I am actually getting like 12
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Old 01-26-2014, 09:57 AM   #15
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So instead of 14 I am actually getting like 12
well now that you mentioned it, it would make sense that you are getting less mpg because the farther you go on a tank the better so if its reading your going farther than you actually are I believe that it would show up as a lower amount than what you figured before you discovered that it was off by 5
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Old 01-26-2014, 10:01 AM   #16
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what motor do you have?
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Old 01-26-2014, 10:02 AM   #17
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Nope if do to speedo gear wrong for tire and gear ratio

If reading slower than actual speed then odometer reads lower than true and you went more miles than indicated and your calculated mpg is is lower then actual mpg

BUT if do to wrong speedo gear for tires and axle ratio your speedo is reading higher than actual then the odometer reading is higher then true and your real distance traveled is less than odometer reading so using odometer for distance calculated a gets a false high MPG and real MPG is LOWER then your calculation using odometer reading

Of course faulty speedo rather than wrong speedo gear might mean speedo reading off and odometer not off

Just use GPS to get true distance traveled and compare to odometer reading

But like I said if speedo and odo are reading higher than true and you use odo reading to calculate MPG actual true MPG is WORSE than calculated
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Old 01-26-2014, 10:03 AM   #18
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Check you Upstream O2 Sensor, a fried sensor will sometimes not throw a code and cause your jeep to get lower mpg. Also.. don't use bosch when replacing, our jeeps seem to be picky about these, stick with factory NGK.
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Old 01-26-2014, 10:05 AM   #19
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what motor do you have?
I have the 4.0.

What is the correct size speedo gear for 30" tires 3.73 and the 4.0 with a 3 speed auto?

So is there anything I can do to get better mpg?
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Old 01-26-2014, 10:05 AM   #20
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Check you Upstream O2 Sensor, a fried sensor will sometimes not throw a code and cause your jeep to get lower mpg. Also.. don't use bosch when replacing, our jeeps seem to be picky about these, stick with factory NGK.
How would I check that
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Old 01-26-2014, 10:07 AM   #21
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ok that makes more sense its too early for me lol my brain I believe has blown out the back of my head from all the thinking I'm trying to do
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Old 01-26-2014, 10:11 AM   #22
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ok that makes more sense its too early for me lol my brain I believe has blown out the back of my head from all the thinking I'm trying to do
Sorry but thanks for your help
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Old 01-26-2014, 10:12 AM   #23
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How would I check that
sometimes if you take it and have an auto parts store hook it up to there computer and can show that the o2 sensor is bad or going bad
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Old 01-26-2014, 10:14 AM   #24
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sometimes if you take it and have an auto parts store hook it up to there computer and can show that the o2 sensor is bad or going bad
Ok thanks
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Old 01-26-2014, 10:17 AM   #25
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Ok thanks
No problem, I would call ahead though to make sure they got the equipment to do it with I always take mine to advanced auto
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Old 01-26-2014, 11:16 AM   #26
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What would the correct speedo gear be
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Old 01-26-2014, 11:29 AM   #27
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What would the correct speedo gear be
here is a link I found idk if it would help or not but it has a chart for gear ratio and mpg Tire & Gear Ratio Chart at Morris 4x4 Center
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Old 01-26-2014, 11:31 AM   #28
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Quadratec has an online chart but easiest was is get a tablet or smartphone with GPS or a hand held GPS and compare actual gps speed to speedo

The pull your speedo gear and count teeth

Now take actual speed and divide by speedo speed

Finally take number teeth on your current gear and divide by number you got in ratio actual to speedo and round to nearest whole number that is tooth count you want

Made up example

GPS speed 66 and speedo speed 60
66/60=1.1

Say you have a current gear with 40 teeth

40/1.1= 33.36 so 33 tooth would be closest
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Old 01-26-2014, 11:31 AM   #29
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What would the correct speedo gear be
here is another chart I just found on the same site Jeep Speedometer Gears at Morris 4x4 Center
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Old 01-28-2014, 12:11 AM   #30
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My speedo is off it says that I'm going 5 mph faster than I am going.
At what speed? Your question is unanswerable without that information.

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