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-   -   Why am i getting such bad mpg (http://www.wranglerforum.com/f282/why-am-i-getting-such-bad-mpg-184753.html)

Bamafan4life 09-03-2012 05:46 PM

Why am i getting such bad mpg
 
Hey i was wondering why i was getting such bad mpgs? Im getting around 10 mpg, i have a 02 with 4.0 and auto transmission. I have a 3.25 suspension lift with 33" tires, could it be that i only have 3.07 gears? I am getting close to 120,000 miles and the spark plugs i dont think have ever been changed. Im using 10w30 oil every 3000 miles and the air filter is clean. Any help to help me get better mpgs would be apreciated, and if your rig's set up is somewhat identical to mine tell me what your getting.

snowbrd84 09-03-2012 05:52 PM

Write a letter to your congressman and hope that some day we quit mandating that corn be put in our gas. When that day comes, you will atleast see some improvement. Other than that, check your catalytic converter, it might be clogged.

The-Judge 09-03-2012 05:58 PM

I have a 02 wrangler with the 4.0 standard trans. I get between 14 and 15 MPG with 31 x 10.5 's.

orange05tj 09-03-2012 05:59 PM

Your driving a brick.

finneyjr 09-03-2012 06:27 PM

Quote:

Originally Posted by orange05tj
Your driving a brick.

I have a 04. I6, 5 speed & was getting 15 mpg on regular gas. I am on my second tank of no ethanol gas. First tank got 19.5 mph with no ethanol. With the cost per gallon more, it still drops operating cost from .25 cents per mile to .18 cents per mile.

Water Dog 09-03-2012 06:30 PM

If you are running 33" tires and haven't done a new speedo gear (or gear change), then you odometer is going to be off as well as your speedometer. That would account for "part" of your bad mileage (reading) problem. The other part (real mileage) would be the 33's with 3:07 dif gears. With that gearing you are not even close to being in your optimum power band.

sdptrey 09-03-2012 06:32 PM

try changing spark plugs you might get a little more, Check tire pressure. Air filter

wellbuilt 09-03-2012 07:19 PM

120 ,000 on original plugs and you are worried about fuel economy ?
Change your plugs you will save the plug money in a tank of fuel.
you speedo is off 3 mil per gallon i bet and you are lousing 3 mils to the gallon with the lack of maintenance .

Patrick H 09-03-2012 08:05 PM

It doesn't make much sense to question poor fuel economy when you don't know the condition of your spark plugs.

shanes04wrangler 09-03-2012 08:38 PM

change the plugs for a start, did mine at 120k when i bought my jeep and iam sure they were the originals and they were done for.

mrcarcrazy 09-03-2012 08:40 PM

do a basic tuneup. You, as noted earlier, are driving a brick. Adjust the lead content of the throttle foot.

10mpg is low, even for a brick...unless you drive like a 16 yr old.

Have you checked for trouble codes? (assuming the CEL isn't illuminated, and is functional)

If the Jeep has cruise, does it work?

shanes04wrangler 09-03-2012 08:45 PM

yea 10mpg is bad, I have a heavy foot and i am getting around 14-16mpg 220-240mpg to the tank

autopc25 09-03-2012 08:56 PM

MPG for 2.5L with automatic and A/C on all the time?
 
Have a stock '97 Sport 2.5L, with A/C, new rebuilt automatic transmission, hard top, +1" height suspension. 225/75-15 BRIDGESTONE DUELER A/T D695 tires at 35psi. Recent tune-up. It has been hotter then normal so I have been driving with the A/C on everyday. I have been averaging about 13 MPG in city bumper to bumper driving lately. I think I used to get over 15-16 MPG before the heatwave this summer? Is this normal for a 2.5L automatic with A/C on all the time?

bc3_Jeep 09-03-2012 09:24 PM

May I suggest switching to a Prius????? My YJ 2.5 with 31s....no mods...AX5....ragtop...non-16 year old driving....60 mile commute daily....gets around 15mpg give or take.......corn content or not......corn IS NOT the problem.....nor is it the solution....... the solution is driving what you NEED instead of what you WANT....if you WANT mpgs.... you NEED a PRIUS........

vertical horizons 09-03-2012 10:12 PM

Quote:

Originally Posted by Water Dog (Post 2754449)
... The other part (real mileage) would be the 33's with 3:07 dif gears. With that gearing you are not even close to being in your optimum power band.

Running 33's, what differential gears should he be running, to be at optimum power?

vertical horizons 09-03-2012 10:14 PM

Quote:

Originally Posted by snowbrd84 (Post 2754306)
... check your catalytic converter, it might be clogged.

Other than taking the catalytic converter down, how do you check it to see if it's clogged?

BrentR94 09-03-2012 10:16 PM

I was just having trouble with mpg with my 98 and I found out that the Catalytic Converter was clogged... I in clogged it and now it gets great mpg... Just a suggestion to look into.
Brent

Bamafan4life 09-03-2012 10:20 PM

Ive only been driving this jeep for about 6 months, my brother was the owner before me and i got to thinking that he never had the plugs changed, today was the first time i thought Of this, i guess ill go buy spark plugs and wires and get my 83 year old uncle to teach me before it gets to cold for him to get out. Im 17 and its time i learn lol

Bamafan4life 09-03-2012 10:25 PM

Quote:

Originally Posted by bc3_Jeep (Post 2755120)
May I suggest switching to a Prius????? My YJ 2.5 with 31s....no mods...AX5....ragtop...non-16 year old driving....60 mile commute daily....gets around 15mpg give or take.......corn content or not......corn IS NOT the problem.....nor is it the solution....... the solution is driving what you NEED instead of what you WANT....if you WANT mpgs.... you NEED a PRIUS........

I dont expect to get 30mpg, but 10 is horrible Id like to get atleast the 14-16 everybody else is getting, and im 17 but drive like im 71 im always atleast 5 miles below the speed limit and dont speed out ethier

SurfKaster 09-03-2012 11:05 PM

At a 120K there's a good chance your O2 sensors are original. I'd look into replacing your upstream sensors along with a new set of plugs to start.

snowbrd84 09-04-2012 07:45 AM

Quote:

Originally Posted by bc3_Jeep (Post 2755120)
May I suggest switching to a Prius????? My YJ 2.5 with 31s....no mods...AX5....ragtop...non-16 year old driving....60 mile commute daily....gets around 15mpg give or take.......corn content or not......corn IS NOT the problem.....nor is it the solution....... the solution is driving what you NEED instead of what you WANT....if you WANT mpgs.... you NEED a PRIUS........

YOU ARE NOT ANSWERING ANY QUESTION.

And CORN IS THE PROBLEM. It contains 33% LESS energy content than pure gasoline and thus get significantly worse economy. Not to mention it damages engines that werent designed to run on it.

OP, go to this site and see if there is a station near you that sells 100% gas with 0% ethanol

pure-gas.org : ethanol-free gas stations

vertical horizons 09-04-2012 08:06 AM

Quote:

Originally Posted by snowbrd84 (Post 2756263)
... go to this site and see if there is a station near you that sells 100% gas with 0% ethanol

pure-gas.org : ethanol-free gas stations

Very informative website.

However, I checked the website against where I live.
It amazes me that, even though Houston is so close to all those refineries, the closest "pure gas" gas station is 74 miles from my house.

And, according to the website, there is not one of those gas stations from Houston to Galveston. :rolleyes:

Great website, though.
It'll come in handy when travelling.

UnlimitedLJ04 09-04-2012 08:07 AM

did you recalibrate the speedo for the larger tires?

miketx 09-04-2012 08:24 AM

If you are thinking about doing the plugs....and you suspect they have never been changed, you might as well do the cap/rotor/wires also. My Jeep had 99k miles on it when I got it. I did all these items and it ran better immediately. I didn't get a drastic bump in mpg, but it performed much better.

James249G 09-04-2012 08:52 AM

Quote:

Originally Posted by vertical horizons (Post 2755334)
Other than taking the catalytic converter down, how do you check it to see if it's clogged?

X2... Anyone do a write up?

Jerry Bransford 09-04-2012 09:17 AM

Quote:

Originally Posted by Bamafan4life (Post 2754280)
Hey i was wondering why i was getting such bad mpgs? Im getting around 10 mpg, i have a 02 with 4.0 and auto transmission. I have a 3.25 suspension lift with 33" tires, could it be that i only have 3.07 gears? I am getting close to 120,000 miles and the spark plugs i dont think have ever been changed. Im using 10w30 oil every 3000 miles and the air filter is clean.

Yep your 3.07 gearing is causing your engine to run at too low of an RPM which is making it lug and run less efficiently.

Be wary on what spark plugs you install, 2000 and newer 4.0L engines are fussy about what spark plugs they run well on. Three good plugs for your 2002 include the Autolite APP985 (NOT the AP985), Champion 7034 (NOT the 3034), or Autolite XP985. The first two plugs are double-tipped platinums, the last one is iridium-tipped and the best of the three.

Quote:

Originally Posted by Water Dog (Post 2754449)
If you are running 33" tires and haven't done a new speedo gear (or gear change), then you odometer is going to be off as well as your speedometer. That would account for "part" of your bad mileage (reading) problem. The other part (real mileage) would be the 33's with 3:07 dif gears. With that gearing you are not even close to being in your optimum power band.

X2 on all that. At least recalibrate your speedometer which takes five minutes to do with a new snap-in plastic speedometer gear which only takes a 1/2" wrench to instal. Your 33" tires are causing your speedometer to erroneously indicate you're driving slower and a shorter distance than you really are. Here's how...

http://www.jeepin.com/features/speedogear/index.asp

Quote:

Originally Posted by vertical horizons (Post 2755326)
Running 33's, what differential gears should he be running, to be at optimum power?

For 33" tires and his 3-speed automatic, 4.10 is the optimal ratio.

Quote:

Originally Posted by Powder Monkey (Post 2755595)
At a 120K there's a good chance your O2 sensors are original. I'd look into replacing your upstream sensors along with a new set of plugs to start.

Yes indeed on all points. When the 02 sensor goes bad, and they do go bad eventually, it usually erroneously indicates to the computer the air/fuel ratio is too lean so the computer then richens the ratio to the point it is full-rich and your mpg goes down the drain.

pwroth58 09-04-2012 01:22 PM

Great info here! What is the optimal gear for the same setup only with the 5 speed manual transmission instead of the automatic?

Jerry Bransford 09-04-2012 02:11 PM

Quote:

Originally Posted by pwroth58 (Post 2757394)
What is the optimal gear for the same setup only with the 5 speed manual transmission instead of the automatic?

4.56 for 33" tires when you have the 4.0L engine and 5-speed transmission. :)

269jeep 09-04-2012 04:18 PM

Change those plugs!!! Then you might want to find out what gears you have.

snowbrd84 09-04-2012 04:57 PM

To determine what gears you have

Go for a drive on the highway, get up into your top gear and reach an RPM of about 2000 or more. Note the RPM and Speed. The speed needs to be the actual speed according to a GPS as your speedo may not be correct unless you have stock everything.

Then use this equation where Tire diameter is (inches), RPM is as displayed on your tach, and speed is in the actual mph according to a GPS.

Gear Ratio = [(RPM x 3.14 x Tire Diameter x 60) / (12*5280)] / Speed


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