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Old 02-22-2014, 04:37 PM   #1
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Gas Mileage

I just checked the gas mileage on my 99 Wrangler 4.0L A/T and I am only getting 10mpg. This seems low am I not right?

I decided to check the plugs; took 3 of the 6 out and they are looking great. I checked the distributor and rotor button and they look great. The vehicle isn't burning excess fuel from sniff testing the exhaust. No black smoke. This vehicle runs like a new one.

My old YJ with 258 6cyl did better than this. What am I missing here? What can I check?

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Old 02-22-2014, 04:56 PM   #2
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Tire size and gearing?

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Old 02-22-2014, 04:59 PM   #3
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gas mileage

tires are 31x10.50 gearing have no clue......99 Jeep Wrangler Sahara
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Old 02-23-2014, 01:55 PM   #4
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Any ideas?
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Old 02-23-2014, 02:08 PM   #5
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Bad O2 sensor maybe?? They can mess with how the computer sends fuel to the engine when they start to go bad.

Someone else can verify, I think it's the upstream ones that can cause issues. There are also specific brands to use and done to avoid.
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Old 02-23-2014, 02:17 PM   #6
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jeep gas mileage does sux.....but, what your experiencing is really bad! Do some research on the O2 sensor.

I get 10 MPG in my F150 Eco-Boost pulling a 26 ft TT!
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Old 02-23-2014, 09:51 PM   #7
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Even if you have 3.07 gears, with 31s you should be getting better mileage. I'd go to a good shop and have them run a diagnostic followed by a real tune up.
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Old 02-23-2014, 10:04 PM   #8
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Originally Posted by Mdaddyrabbit View Post
tires are 31x10.50 gearing have no clue......99 Jeep Wrangler Sahara
Check on the diff cover. There should be a data plate on the left side that will tell you the gearing. Good luck!
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Old 02-24-2014, 03:56 AM   #9
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Originally Posted by Mdaddyrabbit View Post
I just checked the gas mileage on my 99 Wrangler 4.0L A/T and I am only getting 10mpg. This seems low am I not right?

I decided to check the plugs; took 3 of the 6 out and they are looking great. I checked the distributor and rotor button and they look great. The vehicle isn't burning excess fuel from sniff testing the exhaust. No black smoke. This vehicle runs like a new one.

My old YJ with 258 6cyl did better than this. What am I missing here? What can I check?
How did you calculate mileage? Just checking because there are constantly mileage threads and when it comes down to it some people do not calculate it correctly.

- First as asked above, what size tires do you have (if they are not stock (larger) and the speedometer gear is not correct, the recorded miles may be low)

Calculate mileage:

- Fill tank (to the same level each time as best as possible. same station/pump to first click off)

- Reset trip odometer.

- Drive using most of tank

- Refill and divide the number of miles driven by gallons on the refill

- Repete the above several time for a good average
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Old 02-24-2014, 07:47 AM   #10
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If you're running 31's your probably reading 5mph under what you are really running and your mileage will be off also. If you have a GPS, set the mileage counter when you fill up, then at your next fill up, check the MPG off the mileage on the GPS. You will probably be surprised.
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Old 02-24-2014, 09:45 PM   #11
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figuring gas mileage

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Originally Posted by Neil F. View Post
How did you calculate mileage? Just checking because there are constantly mileage threads and when it comes down to it some people do not calculate it correctly.

- First as asked above, what size tires do you have (if they are not stock (larger) and the speedometer gear is not correct, the recorded miles may be low)

Calculate mileage:

- Fill tank (to the same level each time as best as possible. same station/pump to first click off)

- Reset trip odometer.

- Drive using most of tank

- Refill and divide the number of miles driven by gallons on the refill

- Repete the above several time for a good average
I filled up to it would not hold anymore, I then drove until it was close to empty then filled back up. Took the amount of miles and divided it by the amount of gallons it took to fill back up....
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Old 02-25-2014, 02:10 PM   #12
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I filled up to it would not hold anymore, I then drove until it was close to empty then filled back up. Took the amount of miles and divided it by the amount of gallons it took to fill back up....
That's correct.
Also just checking--you were in 2H the whole time and not 4H, right? The only time I've ever been under 11mpg was when we had a ton of snow/ice here and I was in 4H for a few weeks straight.

But you should also do your calculation several times to get an average. Sometimes when I fill up, the gas shuts off really early, so I can get a bad reading if I'm not careful. Do it 3 or 4 times to get a good average fuel economy.
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Old 02-25-2014, 02:46 PM   #13
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I'm running stock gears with 31's. If I use the ethanol added blend, I get 10-12 mpg.
If I run the non ethanol, I get 14-16. My speedometer is right on with radar signs and my gps. <which I think is odd> But the two together can't be wrong.
More things to consider is winter blend gas.
Do you let your vehicle warm up?
Highway vs. stop n go.
Do you drive over 60 mph? <I get best mileage at 60>
Have you disconnected your - battery terminal and had your Jeep re-learn your driving pattern?
1st 200 starts driven up to at least the first degree marker on your temp gauge after disconnecting.
Is your air filter dirty?
Is the strainer bag on your fuel pump clogged?
Are your tires inflated properly?
Is there any brake pull?
Is your alignment straight?
How windy is it?
These are all factors in mpg also.
Yes, you do not buy a Jeep for good gas mileage.
Are your springs and shocks good?
Is there any type of lift?
Search the threads, there are many posts on this subject, and you will find all of these comments, questions, and answers in them.
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Old 02-25-2014, 05:19 PM   #14
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i would love to get non ethanol gas but its not sold near me...
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Old 03-01-2014, 04:59 PM   #15
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I decided to drive the wrangler to the shop and have it checked out since I filled up and it took 1.5 tank of gas to go 40 miles this week. They put it on the machine and ran the sensors and electronics through the test and nothing shows bad. The owner told me he would disconnect the O2 sensor and see what it did next week. I hope the O2 is the problem I to get more than 80 miles per tank of gas.
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Old 03-03-2014, 04:19 AM   #16
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80 mi per tank? That would mean you are getting 5 mpg or less depending which tank you have (15 or 19 gal)
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Old 03-03-2014, 10:17 AM   #17
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FWIW, I have a 4.0/5speed dana44/3.73 and get 15mpg almost on the nose.
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Old 03-03-2014, 09:28 PM   #18
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I drove it yesterday and today and it appears to be doing better with the O2 sensor unplugged. I sure hope that is whats wrong. If it is I can spend $50 bucks and save a fortune.
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Old 03-13-2014, 12:48 PM   #19
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I filled back up today and calculated my gas mileage to be 10.5 MPG. The OBD shows no errors except that I have the upstream O2 sensor unplugged. Do you guys have any suggestions? I am going to need to part this thing because I cannot afford $3.44 fuel for it.
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Old 03-13-2014, 03:04 PM   #20
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drive smarter...
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Old 03-13-2014, 03:23 PM   #21
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Wow Thanks

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drive smarter...
Thanks for a clueless comment....I will bet you that you are a ID10T error in the making. LOL
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Old 03-13-2014, 04:00 PM   #22
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Thanks for a clueless comment....I will bet you that you are a ID10T error in the making. LOL
I get what he's saying, shift early, easy on the gas, stay in 5th (6th if ya got it).
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Old 03-13-2014, 04:35 PM   #23
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I get what he's saying, shift early, easy on the gas, stay in 5th (6th if ya got it).
So manually shift an automatic transmission.......When I started the thread I listed the wrangler was automatic. If that is what he meant then he didn't read the the thread starter.....not trying to disrespectful but reading replaces misconception.
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Old 03-13-2014, 04:47 PM   #24
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Have you checked the odometer against GPS or mileage indicators on the freeway as mentioned earlier? If your odometer is off your calculation will be off.

I average 12.5-13 mpg with the 4.0 auto/33x12.5 tires and 3.73 gears.
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Old 03-13-2014, 04:49 PM   #25
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Have you checked the odometer against GPS or mileage indicators on the freeway as mentioned earlier? If your odometer is off your calculation will be off.

I average 12.5-13 mpg with the 4.0 auto/33x12.5 tires and 3.73 gears.
I have not checked against GPS or mile markers. I am going to do that Saturday.

How do I figure out what gears I have in mine?
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Old 03-13-2014, 04:59 PM   #26
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To get semi-close, jack up the rear end, mark a tire with chalk and mark the driveshaft. Rotate the tire one full revolution and count how many times the driveshaft rotated. If its just past 3 you've got 3.07, if it was almost but not quite 4 you've got 3.73, if it was just past 4 you've got 4.10, etc.
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Old 03-13-2014, 05:13 PM   #27
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Read post #8 ref where to locate gear info.
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Old 03-13-2014, 05:16 PM   #28
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Originally Posted by Mdaddyrabbit View Post

So manually shift an automatic transmission.......When I started the thread I listed the wrangler was automatic. If that is what he meant then he didn't read the the thread starter.....not trying to disrespectful but reading replaces misconception.
No, he was just saying drive smarter. Accelerate slower, don't be as aggressive, keep it around 60, don't stay on the gas all the way up to stop signs and brake at the last moment!

Just using those techniques, I can boost my mileage 30%. I get 12mpg driving "normally" but if I really try, I can push nearly 16mpg out of it.

The thing is, it's not worth it for me. The jeep is my fun vehicle, so I burn all the gas I want in it. I have a civic for road trips and commuting to school every day.
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Old 03-13-2014, 07:00 PM   #29
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You never did say where your at, if your letting it warm up for a little bit that could be part of it. I've got an 03 with the 4.0, manual tranny, and regeared it to 4.56 with the correct speedo. I get anywhere from 10.5-13 depending upon how I drive and how long I let it warm up. The winter blend of gas did cause my mpg to go down as well but that's part of having a jeep. There definitely not aerial dynamic so they suck on gas mileage.
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Old 03-13-2014, 07:17 PM   #30
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You never did say where your at, if your letting it warm up for a little bit that could be part of it. I've got an 03 with the 4.0, manual tranny, and regeared it to 4.56 with the correct speedo. I get anywhere from 10.5-13 depending upon how I drive and how long I let it warm up. The winter blend of gas did cause my mpg to go down as well but that's part of having a jeep. There definitely not aerial dynamic so they suck on gas mileage.
Warm up? As soon as the oil pressure is up away I go, it warms up faster if you drive it and I get good heat in a couple of miles. Plus you do not waste any gas waiting for it to warm up, you use that gas to increase your mpg totally. Been driving that way for over over 45 years.

To make the wife happy when we commuted together I bought heated carbon fiber seat covers and they were fantastic. Got laid off 2 years ago and now have no need to leave the house when it's cold out except to get more beer.

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