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Topic Review (Newest First)
09-16-2012 11:17 AM
autopc25
Quote:
Originally Posted by Tdog02 View Post
Depends on the state of the fuel system. You might want to pull the fuel rail and injectors and clean them out. It couldn't hurt. I've been reading about injector upgrades for a few months and most who post about changing them out talk about gunk build up in the rail. Maybe a restriction, poor atomization of fuel, etc... Maybe have a caliper dragging or engine control issues from bad sensors, or restricted cats. Have you had any luck with a diagnosis or fix? Post it up and let us know before the corn cobs start flyin
Another very good place to check. A bad caliper that is sticking or dragging can kill mileage.
09-16-2012 11:15 AM
autopc25
Quote:
Originally Posted by Bamafan4life View Post
I had one code, evedently, my engines suckin in air somewhere its not supposed to, must be a hole somewhere in my vent, going to try to locate it tommarrow. Also going to get the price of plugs and will talk to my mechanic about regearing the next time i see him
Everyone knows Jeeps do not get good MPG compared to regular SUV or cars. They need to be kept in top tune to get the best mileage they can possibly get.

I just went down this path. Used to get 15 mpg and it dropped to 11 recently. It has been hotter this year then ever and I have had the A/C on all the time so that does not help. But I suspected something else was also wrong? I replaced everything, full tune-up w/Mopar parts, Mopar 02 sensor (had Bosch), new distributor (bad bushing), cam position sensor, checked cat converter, replaced muffler. The old muffler was smaller and had smaller diameter pipes going in. Maybe it was a little plugged or something? Surprisingly I got +2 mpg with a new muffler. With the muffler I got up to 13 mpg, still not right?

I also checked obvious locations for vacuum leaks and found nothing.

Yesterday I replaced all of my old injectors that had 160K on them with Bosch 4-port injectors. One was leaking.

I also replaced my valve cover gasket. This is where I found something weird. All of the studs that hold down the valve cover were hand loose! The factory uses RTV only to seal no gasket. That works but over time the RTV must shrinks away. The thickness of the RTV bead shrinks so the valve cover is no longer tight. This might be a possible source of a vacuum leak?
09-15-2012 08:55 PM
Rwilliamjacob Your top could be worn out and it is creating drag. Plus you are using 3.23's with 33's
09-15-2012 08:45 PM
Tdog02 Depends on the state of the fuel system. You might want to pull the fuel rail and injectors and clean them out. It couldn't hurt. I've been reading about injector upgrades for a few months and most who post about changing them out talk about gunk build up in the rail. Maybe a restriction, poor atomization of fuel, etc... Maybe have a caliper dragging or engine control issues from bad sensors, or restricted cats. Have you had any luck with a diagnosis or fix? Post it up and let us know before the corn cobs start flyin
09-11-2012 10:03 AM
jeepndon
Quote:
Originally Posted by snowbrd84 View Post
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
Corn is not the PROBLEM as someone else can get 15 to 16 and he gets 10MPG. he should be getting the same MPG as everyone else who runs corn.
09-11-2012 10:01 AM
jeepndon
Quote:
Originally Posted by Bamafan4life View Post
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.
Wow so many different options on what to check. Its simple first change the spark plugs nothing too fancy just some NGK or champion plugs make sure to gap them to .035. replace the wires and if your jeep has a cap and rotor setup than replace them too. this will be the cheapest option see if it improves the economy and power you get.
09-09-2012 09:18 PM
James249G
Quote:
Originally Posted by vegasjeeper
you don't buy a jeep for mileage, you buy it for the coolness and fun factor, and chicks dig em.
x2
09-09-2012 06:38 PM
Capp35 I am getting ready to put on 32" (265/75/16). I have a 4.0 auto with a Dana 44 and 3.73 rear gear. I am figuring my gearing should be just right on with this setup.
Any feedback otherwise?
09-08-2012 06:39 AM
xxBOsoxFANxx
Quote:
Originally Posted by Jerry Bransford View Post
4.56 for 33" tires when you have the 4.0L engine and 5-speed transmission.
See, this is why I love this forum...I was wondering this myself and now I don't have to start a thread to find the answer!
09-08-2012 04:46 AM
VEGASJEEPER You don't buy a Jeep for mileage, you buy it for the coolness and fun factor, and chicks dig em.
09-08-2012 12:46 AM
Bamafan4life I had one code, evedently, my engines suckin in air somewhere its not supposed to, must be a hole somewhere in my vent, going to try to locate it tommarrow. Also going to get the price of plugs and will talk to my mechanic about regearing the next time i see him
09-05-2012 06:43 AM
Tdog02
Quote:
Originally Posted by Bamafan4life
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.
You have gotten some great info so far. Have you changed your fluids? I have been going through my new to me 02 4.0/auto and doing maintenance on everything. Recently I installed the deeper transmission pan on the 32RH. The new fluid made a difference at the pump. I have also started using an ethanol stabilizer in hopes of neutralizing the effects of that crap, it really does kill fuel mileage.
09-05-2012 01:51 AM
pwroth58 Thanks Jerry!
09-04-2012 08:04 PM
snowbrd84
Quote:
Originally Posted by Jerry Bransford View Post
That method is only accurate when the transmission is not in Overdrive. I.e. in 4th gear if it's a 5-speed, 5th gear if it's a 6-speed, or after turning the Overdrive off if it's the 42RLE 4-speed automatic.
My jeep isnt fancy enough to have overdrive, i was only blessed with three gears
09-04-2012 06:47 PM
Jerry Bransford
Quote:
Originally Posted by snowbrd84 View Post
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
That method is only accurate when the transmission is not in Overdrive. I.e. in 4th gear if it's a 5-speed, 5th gear if it's a 6-speed, or after turning the Overdrive off if it's the 42RLE 4-speed automatic.
09-04-2012 06:47 PM
Jerry Bransford
Quote:
Originally Posted by snowbrd84 View Post
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
Only true when the transmission is not in Overdrive. I.e. in 4th gear if it's a 5-speed, 5th gear if it's a 6-speed, or after turning the Overdrive off if it's the 42RLE 4-speed automatic.
09-04-2012 06:09 PM
Capp35
Quote:
Originally Posted by snowbrd84 View Post
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
Why not just read the tag on the pumpkin?
09-04-2012 04:57 PM
snowbrd84 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
09-04-2012 04:18 PM
269jeep Change those plugs!!! Then you might want to find out what gears you have.
09-04-2012 02:11 PM
Jerry Bransford
Quote:
Originally Posted by pwroth58 View Post
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.
09-04-2012 01:22 PM
pwroth58 Great info here! What is the optimal gear for the same setup only with the 5 speed manual transmission instead of the automatic?
09-04-2012 09:17 AM
Jerry Bransford
Quote:
Originally Posted by Bamafan4life View Post
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 View Post
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 View Post
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 View Post
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.
09-04-2012 08:52 AM
James249G
Quote:
Originally Posted by vertical horizons View Post
Other than taking the catalytic converter down, how do you check it to see if it's clogged?
X2... Anyone do a write up?
09-04-2012 08:24 AM
miketx 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.
09-04-2012 08:07 AM
UnlimitedLJ04 did you recalibrate the speedo for the larger tires?
09-04-2012 08:06 AM
vertical horizons
Quote:
Originally Posted by snowbrd84 View Post
... 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.

Great website, though.
It'll come in handy when travelling.
09-04-2012 07:45 AM
snowbrd84
Quote:
Originally Posted by bc3_Jeep View Post
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
09-03-2012 11:05 PM
SurfKaster 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.
09-03-2012 10:25 PM
Bamafan4life
Quote:
Originally Posted by bc3_Jeep View Post
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
09-03-2012 10:20 PM
Bamafan4life 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
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