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Old 08-30-2012, 02:16 PM   #1
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Getting 7 miles to the gallon?

I have a '98 TJ and I am only getting 7 miles to the gallon. I have changed the spark plugs but I can not really tell a difference. If anyone has any suggestion please let me know!

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Old 08-30-2012, 02:28 PM   #2
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What's the Tire size, is it a manual, what gears, and how much extra stuff do you have on it like a new bumper, winch, hardtop?

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Old 08-30-2012, 02:33 PM   #3
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I am running a 31x10.50x15 BF Goodrich Mud Terrain Tire, It is a automatic 2.5L, Soft Top,
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Old 08-30-2012, 02:34 PM   #4
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Stock gears?
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Old 08-30-2012, 02:36 PM   #5
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Yes, stock as far as I know!
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Old 08-30-2012, 02:37 PM   #6
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Oil change, spark plugs, clean throttle body, air filter, distributor cap cleaning/replacement, spark plug wires?

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Old 08-30-2012, 02:40 PM   #7
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Ill stop complaining about my 10mpg....
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Old 08-30-2012, 02:41 PM   #8
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Well it shouldn't make a big difference, you only have 31s, I guess wait til someone else that has more experience. I have 2.5 with 35s and I get about 15 a gallon.
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Old 08-30-2012, 02:43 PM   #9
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Along with my previous list, when was the last time your diffs, transfer case and transmission were serviced? Friction in those locations wont help either.
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Old 08-30-2012, 02:59 PM   #10
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Driving style has alot to do with MPGs. Do you drive like an old lady to church on Sunday ??? Or a teenager who "borrowed". His dads corvette??
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Old 08-30-2012, 03:00 PM   #11
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What rpm does it idle?
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Old 08-30-2012, 03:33 PM   #12
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showing this to my wife so she stops complaining about my 14mpg
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Old 08-30-2012, 06:15 PM   #13
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showing this to my wife so she stops complaining about my 14mpg
I showed my wife to too but she said her Samurai gets 30mpg so i still need to get a second job to pay for my gas...lol

Check your air filter and check all your vacuum lines for leaks.
do a compression test to make sure your motor is in good shape.
It should get around 15 or better.

If none of this helps plan your trips with lots of down hill roads and coast.
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Old 08-30-2012, 06:56 PM   #14
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I showed my wife to too but she said her
It should get around 15 or better.
That is what I average with 31x10.5 in my 97 2.5 auto... That is running a/c with Hardtop..
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Old 08-30-2012, 08:04 PM   #15
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Wow! You'd think if it was running that poorly the check engine light would be glowing in the dash. The 2000 2.5 5-speed I previously owned got 17 with 32" mudders and 19 with 30" street tires, but from what I see here in comparison mine was some kind of freak. Probably wouldn't hurt to have someone plug into it with a scanner. Something isn't right.
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Old 08-30-2012, 08:05 PM   #16
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check your exhaust also..stopped up cat converter kills power and gas mileage
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Old 08-30-2012, 08:11 PM   #17
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keep rpms below the 2k mark. drive without air conditioner. i used to get 22 before i got the AC fixed and got an after market radio, and a new bumper, now i get 17.
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Old 08-30-2012, 08:19 PM   #18
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get bigger tires,add racing stripes on the sides and cram a potato in the tailpipe.it can't be any potato though it has to be an Idaho potato. you should see a huge difference in MPG.

















































it might be more or less.....prolly less
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Old 08-30-2012, 09:22 PM   #19
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get bigger tires,add racing stripes on the sides and cram a potato in the tailpipe.it can't be any potato though it has to be an Idaho potato. you should see a huge difference in MPG.

it might be more or less.....prolly less
One of my friends did this, and it worked awesomely! But he didn't use a potato he used a Georgia peach.
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Old 08-30-2012, 09:39 PM   #20
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First off how are you measuring your fuel usage? Odometer or GPS?

If odometer is your spedo correct? If its off by just a few mph it will throw off your odometer thus giving you false numbers

Have you replaced your O2 sensors? If it fails the ECU thinks your running lean and burns more fuel to try to get to optimal mixure.

Is your header cracked? If so you suck in air confusing your O2 sensor making it think your running lean then telling the ECU to dump more fuel.

What temp is your engine running? Below 210 the ECU thinks the engine is cold and will burn more fuel to try to get engine up to operating temp.

What weight oil you running? Too think and your engine has to work harder to pump it.

Air filter have you changed it/cleaned it lately?

Cap/rotor when was the last time you changed that? Corroded thermals can cause misfires

Spark plug wires? Worn wire can cause drop in resistance which in turns causes spark plugs from working to peak perfermance.

Spark plug whats the gaping at? Should be .035

Thats all I got for now.
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Old 08-30-2012, 10:21 PM   #21
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You might have a bad cat converter. I had a very similar issue. I changed the spark plugs and cleaned the throttle body, which made a minor difference, but when I replaced my clogged cat, my MPG jumped up by like 8.
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Old 08-30-2012, 11:26 PM   #22
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You might have a bad cat converter. I had a very similar issue. I changed the spark plugs and cleaned the throttle body, which made a minor difference, but when I replaced my clogged cat, my MPG jumped up by like 8.
I'm of the same mind, if it seems to be running decent and just getting crappy mileage I think the exhaust is plugged up, cat.
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Old 08-31-2012, 04:59 AM   #23
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Yeah,
I'd say it was you cat converter also. Just about no doubt in my mind. As plugged as yours might be, it is probably glowing red when driving! Was on my plugged up cat on my truck.

Cripe! 7 mpg's makes my '66 Plymouth Satellite look awesome!! Even my Jeep get's better than that car! I get about 18-20 with a 5 speed manual and a 4.0L in Jeep.
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Old 08-31-2012, 07:02 AM   #24
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2004 TJ, 33x12.5 Mud Terrains on 15" Wheels, 4" Suspension Lift, Stock bumbers (minus the milk jugs), 5speed Manual... I'm averaging 7 - 10 MPG as per my GPS. Maybe I'll just buy a Jeep Compass!
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Old 08-31-2012, 10:18 PM   #25
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Im running a 4.7L stroker, 4.56 gears with 37s and im getting 14mpg (confirmed by GPS)on top of all that with all my armor and gear i drive around with im pushing 4800lbs my jeep is a tank.
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Old 09-02-2012, 09:02 PM   #26
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I had the jeep checkout Saturday and the mechanic found nothing wrong with cat. converter. He said the timing could us to be adjusted but when he referred to some online material it said it was not adjustable. He also recommend an emissions chip in order to straighten out the timing and gas mileage. What do you all thing about his recommendations?

Thanks,
Corey V.
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Old 09-02-2012, 09:27 PM   #27
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Did the speedo gear get changed? with the larger tire size it will not read right. for an example it says your going 65 and really going 72. that will throw off your calc for mpg and your odometer. hope that helps
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Old 09-02-2012, 09:31 PM   #28
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No, speed is pretty much dead on with gauge.
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Old 09-02-2012, 10:34 PM   #29
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I had the jeep checkout Saturday and the mechanic found nothing wrong with cat. converter. He said the timing could us to be adjusted but when he referred to some online material it said it was not adjustable. He also recommend an emissions chip in order to straighten out the timing and gas mileage. What do you all thing about his recommendations?

Thanks,
Corey V.
Emissions chip? WTF is that? If he's talking about a tune, no tune in the world is going to fix your 7 mpg problem. If I was you i'd clean EVERYTHING (throttle body, PCV, run seafoam through the top-end and in the tank) and do a full tune up (oil, diffs, tranny,all filters). I'd also take the brakes apart and clean/lube them incase you have a sticking guide pin. Do you feel any excess drag?
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Old 09-02-2012, 11:55 PM   #30
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Have advance read your obd2 my guess in O2 sensors by chip he means a performance chip that can change your air to fuel rating in your intake mani but will only give you like 3 to 5 mpg for around 3 or 4 hundred dollars

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