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Old 03-20-2008, 10:59 AM   #1
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Gas mileage problems

hey so i know jeeps dont get great gas mileage, ive heard between 11-13, but right now im getting 5mpg. i took out the spark plugs which were completely covered in carbon, and replaced em, but the jeeps exhaust still smells like gas, anyone no wat else might be wrong??? cuz this low gas mileage is killin me!!!

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Old 03-20-2008, 11:39 AM   #2
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There are a few basic steps I would take to begin with:

1. check air filter and replace if dirty
2. replace fuel filter
3. run a bottle of fuel injector cleaner through a tank of gas
4. spark plugs (you said you have already done that)
5. check all fuel lines (I assume you would notice if you were leaking gas)

These a few basic steps that can improve mgp.

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Old 03-20-2008, 02:21 PM   #3
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hey so i know jeeps dont get great gas mileage, ive heard between 11-13, but right now im getting 5mpg. i took out the spark plugs which were completely covered in carbon, and replaced em, but the jeeps exhaust still smells like gas, anyone no wat else might be wrong??? cuz this low gas mileage is killin me!!!
Sounds like it is running way way too rich to me. I would check o2 sensor, airflow sensor etc. Is the check engine light on? I would not run it too long in this condition as it it will have very negative impact in your catalytic converter!
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Old 03-20-2008, 03:14 PM   #4
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mine's doing the same thing!!! has just done 30miles on 1/4 tank of fuel!!! At $2.20/litre in the UK that is tough
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Old 03-20-2008, 03:20 PM   #5
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mine's doing the same thing!!! has just done 30miles on 1/4 tank of fuel!!! At $2.20/litre in the UK that is tough
That is over $8 a gallon, and I only pay 3.15-3.20 now. Been to england, my Grandmother-in-law lives in manchester. Only paid 95p/liter then and that still sucked. Traffic accident on my birthday....My money does not go far over there. Never seen a jeep over there either.
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Old 03-20-2008, 04:32 PM   #6
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Not too many here, mostly Cherokees. I think there are only about 8000 wranglers in the whole country. Parts are always damn expensive too and I work for one of the only wholesalers that even stock the parts. I find it cheeper to order direct from the states. For example a replacement soft top fabric is sold here for £575 ($1100) it's only $300 in the US!
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Old 03-20-2008, 04:47 PM   #7
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One of the above posts is parially inaccurate. There is no replacable fuel filter on a wrangler, its a one piece fuel pump assembly inside the tank.

It sounds like your issue is an 02 sensor. Ive have that happen to a 4.0 before, with the same results.

After you figure out which 02 sensor went back, and fix it, you still may want to check your plug wires, air filter, and do a fuel system cleaner (the fuel system cleaning guru should chime in here soon) just for safe measure
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Old 03-20-2008, 10:31 PM   #8
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Haha, as far as I know, there's no magic to which fuel system cleaner you use. I think they ultimately all do the same thing.

Your right, you cannot easily replace the fuel filter. As soon as I purchased my TJ I learned that you can only purchase it from the dealer and it comes pre assembled with attached lines. Not to mention what it takes to get to it.
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Old 03-21-2008, 05:31 AM   #9
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Most fuel system cleaners are similar, true, but there is a gentlemen on here (Jerry Bradsworth i believe?) that knows an old school way using water
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Old 03-21-2008, 09:27 AM   #10
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is there en engine light???? id say 02 sensor is the culprit. I have 33s a 3 speed auto, stock 3.73s and i just had a tank of 17 on the highway and 13 while wheeling
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Old 03-21-2008, 09:49 AM   #11
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The other biggie is the thermostat, if your jeeps engine does not reach 185F or above the ECU keeps the engine in cold loop which dumps twice the gas in. Our 97ZJ had a stuck open tstat that came out in pieces when I replaced it back in October. That ZJ was getting about 7mpg on the trip home from New Jersey to home in Pennsylvania.
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Old 03-21-2008, 10:09 AM   #12
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A sudden drop in fuel economy is often nothing more than the upstream (nearest to the exhaust header) 02 sensor has gone bad. When it goes bad, the air-fuel mixture turns full rich so the mpg immediately goes into the toilet. Older TJs have one upstream 02 sensor, newer TJs have two upstream 02 sensors. Being able to smell gasoline is often another symptom of this problem.

Another possible cause would be a clogged (bad) catalytic converter but my first thought is a bad 02 sensor. And they do go bad, they need periodic replacing.
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Old 04-05-2008, 12:18 AM   #13
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A sudden drop in fuel economy is often nothing more than the upstream (nearest to the exhaust header) 02 sensor has gone bad. When it goes bad, the air-fuel mixture turns full rich so the mpg immediately goes into the toilet. Older TJs have one upstream 02 sensor, newer TJs have two upstream 02 sensors. Being able to smell gasoline is often another symptom of this problem.

Another possible cause would be a clogged (bad) catalytic converter but my first thought is a bad 02 sensor. And they do go bad, they need periodic replacing.
would any of these O2 sensors you mentioned throw a CEL ?? My MPG has also gone to crap, but as of now, no CEL.
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Old 04-05-2008, 07:33 AM   #14
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O2 sensors can also get what my friend calls 'lazy' which will not throw a check engine light but will hurt mileage.
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Old 04-05-2008, 09:02 AM   #15
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25.4 mpg in my 2008 Wrangler X (reading right off the gauge on the dash)!

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Old 04-05-2008, 10:41 AM   #16
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could some one hit soupy with a big book or something for coming here and bragging.
lol

As far as ur problem goes i believe its an O2 Sensor too...you can use a scanner and see what the ECU sees (as in data received from the sensors) I believe autozone will do it for free.
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Old 04-05-2008, 10:56 AM   #17
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25.4 mpg in my 2008 Wrangler X (reading right off the gauge on the dash)!

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Is that with the 4 or the 6 cylinder and have they improved it that much ?
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Old 04-06-2008, 05:43 AM   #18
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Just fitted a new O2 sensor (what a simple job!!) and will monitor the milage. There was no fault showing on the diagnostic system (dealer level) but the lamda readings were not changing as quick as one would expect. Hope this helps, next thing is gonna be a map sensor (ouch) Hope your problem is easier to find than mine!!
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Old 04-06-2008, 02:15 PM   #19
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O2s and a "Seafoam" cleaning may help. At 5 mpg replacing both O2s would still be less than a couple tanks of fuel.
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Old 04-06-2008, 04:49 PM   #20
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When my bro first got his Tj he got 175 to a tank. Now he gets 215! with our special additives. Like 18mpg I guess.
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Old 04-06-2008, 05:03 PM   #21
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When my bro first got his Tj he got 175 to a tank. Now he gets 215! with our special additives. Like 18mpg I guess.
how much gas does he put in? i get ~240 a tank before i added my 35s and now believe it or not i think i might be getting better. Currently i have a little more than a half a tank of gas left and my odo measures 115

i still have not corrected my speedo gear so thats 115x1.17=135 miles

I still need to run one tank completely as something always happens lol. My first tank after the 35s i took a trip so it was almost all highway. The tank after that my battery died so my odo reset, this is the 3rd tank of gas i think.
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Old 04-06-2008, 11:12 PM   #22
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how much gas does he put in? i get ~240 a tank before i added my 35s and now believe it or not i think i might be getting better. Currently i have a little more than a half a tank of gas left and my odo measures 115

i still have not corrected my speedo gear so thats 115x1.17=135 miles

I still need to run one tank completely as something always happens lol. My first tank after the 35s i took a trip so it was almost all highway. The tank after that my battery died so my odo reset, this is the 3rd tank of gas i think.
haha youre getting LESS miles than your odo says. which kinda seems IMPOSSIBLE that youre getting BETTER gas mileage after your install of 35's. check your math again.
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Old 04-07-2008, 12:00 AM   #23
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haha youre getting LESS miles than your odo says. which kinda seems IMPOSSIBLE that youre getting BETTER gas mileage after your install of 35's. check your math again.
very funny dude.. i am getting MORE miles than my odo says. My oddo says 115!!! it turns slower so it reads slower therefore 115x1.17 as thats the ratio of the right speedo gear i need vs the one i have...

by that you're saying that after i install my 35s my axles are spinning faster even though i have a bigger radius tires? stock tires my speedo would read let say 60 mph and now when my speedo reads 60 i'm going slower? uuhhh no

impossible is a big word. Try it your self some time.. cruize around town on 2-3 gear and see what mpg you get and then cruize on 5th gear and see what mpg u get.
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Old 04-20-2008, 08:59 AM   #24
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Have just run through a tank of gas and got 280 miles, with a mix of city and highway cruising at 70. Much better since the new O2 sensor. Thanks
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Old 04-20-2008, 11:37 AM   #25
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What kind of age/miles is common for the o2 sensors to need replacing? I'm a bit curious about this b/c I've started to gradually loose some mpg. But the rig only has 50K and is a 2004. Seem to have lost a little power too. Neither symptom is drastic, but power and mpg just doesn't seem to be what it was 6 months ago. And in that same time period the exhaust tip has developed a soot ring at the opening. Dealer just says, "if you drank fuel and then set it on fire in your belly, I bet your exhaust pipe would be black too". Gee thank a-hole. BUT, like the post earlier, I'm not getting any codes.
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Old 04-20-2008, 11:42 AM   #26
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Not too many here, mostly Cherokees. I think there are only about 8000 wranglers in the whole country. Parts are always damn expensive too and I work for one of the only wholesalers that even stock the parts. I find it cheeper to order direct from the states. For example a replacement soft top fabric is sold here for £575 ($1100) it's only $300 in the US!
PLus in England your about 1000% more likely to have some bastard put a knife through it just for fun, thats why i didnt have a soft top while I lived there
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Old 04-20-2008, 12:05 PM   #27
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Have just run through a tank of gas and got 280 miles, with a mix of city and highway cruising at 70. Much better since the new O2 sensor. Thanks
I was happy with mine on Friday, I left Las Vegas, NV and traveled to Fresno, CA a little over 400mi. and averaged 17.4 mpg.
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Old 04-20-2008, 12:07 PM   #28
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PLus in England your about 1000% more likely to have some bastard put a knife through it just for fun, thats why i didnt have a soft top while I lived there
Same here in chicago. People like that deserve to be shot and if moving then shot again!!!
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Old 04-20-2008, 07:35 PM   #29
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What kind of age/miles is common for the o2 sensors to need replacing? I'm a bit curious about this b/c I've started to gradually loose some mpg. But the rig only has 50K and is a 2004. Seem to have lost a little power too. Neither symptom is drastic, but power and mpg just doesn't seem to be what it was 6 months ago. And in that same time period the exhaust tip has developed a soot ring at the opening. Dealer just says, "if you drank fuel and then set it on fire in your belly, I bet your exhaust pipe would be black too". Gee thank a-hole. BUT, like the post earlier, I'm not getting any codes.

Unless you are doing almost exclusively interstate hiway driving you really need to replace your plugs. My 98 XJ's plugs used to last about 80,000mi which for me was almost 2 years, when I would pull them the gap would be between .50 and .55 thousands vs the .35 they are supposed to be.
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Old 04-20-2008, 07:42 PM   #30
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What kind of age/miles is common for the o2 sensors to need replacing? I'm a bit curious about this b/c I've started to gradually loose some mpg. But the rig only has 50K and is a 2004. Seem to have lost a little power too. Neither symptom is drastic, but power and mpg just doesn't seem to be what it was 6 months ago. And in that same time period the exhaust tip has developed a soot ring at the opening. Dealer just says, "if you drank fuel and then set it on fire in your belly, I bet your exhaust pipe would be black too". Gee thank a-hole. BUT, like the post earlier, I'm not getting any codes.
Just replace the upstream o2 senser as this is what controlles the air/fuel. But at 50k I could see them needing to be replaced. I need to pick up a new one as i have 100k on the original one.

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