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Old 11-01-2006, 11:35 AM   #1
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wrangler 2k bad fuel economy

Hello ALL,
We just purchased our 2000 jeep wrangler 4.0 automatic with 64,000 miles, I had it checked out by jeep dealer & they said the jeep was in excellent condition.

My current problem is that I am only getting about 10MPG fuel economy. I was wondering if anyone had similar issue & what should I look into. Mainly driven in the city, I rarely step on the jeep.

my friend suggested that his 91 jeep had bad catayltic converter. I look into changing the converter, does this sound like a good solution.

Thanks in advance,
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Old 11-01-2006, 02:43 PM   #2
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Does your Jeep have any modifications? What size motor? What transmission? If you have bigger tires, and are driving primarily city, that could be right...

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Old 11-03-2006, 10:14 AM   #3
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I have a 02 4.0 with 3.5 inches of lift and 33x12.50 tires that has 75k miles on it, I get around 10-15mpg in the city and around 19 on trips without the use of the AC. A bad cat would probably throw a code in the computer on that model year and turn on the check engine light. When the jeep is running does it smell like fuel around the back by the tailpipe? Or do you notice any drivability problems, even slight ones?
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Old 11-04-2006, 08:56 AM   #4
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I get about 10-12 mpg on mine, but im runnin 38s. You should be gettin alot better then that on yours. My buddy has a 97 with 35s he runs about the same mpg i do. You know what gears you are running or tire size? Need a lil more info about your jeep to really help ya.
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Old 11-04-2006, 07:15 PM   #5
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Could be a number of things. Start with the simple one's. Check the plugs, check the air filter, check the tire pressure. Next time you fill up use a bottle techron fuel injector or fuel system clearner and fill up with High test gas, as it will have some added clearners in it the lower rated gas's do not. If you stock you should be getting much better mpg than 10.
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Old 11-05-2006, 12:06 AM   #6
Knows a couple things...

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First, high octane gasolines have no more fuel cleaners than 87 octane does. That's a myth gasoline manufacturers have no interest in dispelling, the same as the false rumor that high octane boosts power in engines not designed for it... totally untrue too. Running high test gasoline not only won't help clean things out, it can also increase the level of deposits because high octane fuel burns slower and may not combust completely, leaving deposits behind. Octane's purpose is to help it resist premature combustion from compression, that is all. And once again, to be sure, the manufacturers do not add additional amounts of fuel injector cleaners to higher-octane fuels.

Two common causes of suddenly reduced fuel economy include a bad upstream 02 sensor and a bad/clogged catalytic converter. And if the 02 sensor has gone bad, that will produce an ultra-rich fuel condition that not only causes (of course) poor fuel economy but it will also cause the catalytic converter to eventually fail. The unburned gas getting into the cat is the cause of that.

So if the plugs and air filter are ok, I'd be looking at the upstream (nearest the exhaust header) 02 sensor followed by the catalytic converter. Then again, Jeeps are especially sensitive to being driven at fast speeds with a heavy foot so far as fuel economy goes. Make sure your tires are fully aired up too.
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Old 11-05-2006, 04:38 AM   #7
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Certain gas brands do infact have more/a different mix of cleaners than others, and when used with a fuel system/injector cleaner can and do help the system. Then after that go, to 89 or 87 is fine. Also some stations you are not getting 100% gas, its a blend, so when one takes a pragmatic look, one will find that what may be true in one part of the county may not always be the case in others.
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Old 12-20-2006, 12:52 PM   #8
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I own a completely stock 04 Sport 4.L engine with 5 speed. Fuel economy is a sore subject with me. I in no way expect great fuel economy from a Jeep -- If I could get my money back from the purchase, I'd still keep my beloved Jeep -- but it is a sore point.

According to the EPA estimate, my 04 should do 15/19 MPG, city/highway respectively.

My car is well maintained and I drive conservatively with stock road tires and I have consistently done 15MPG maximum in any road condition.

I took the car in to have this subpar performance analyzed and for the 04 the conclusion of the dealer is that ANY condition that would cause poor fuel economy would ALSO result in a fault code being produced. No code, no engine problem. I was advised that 15MPG is actually good for the 04 and that many Jeeps do worse than that. I was also told that there is no aftermarket modification in existence that will improve TJ fuel economy. The mantra was given: If you want fuel economy, don't buy a Jeep.

Anyway, this is just a data point for you. I hope this helps.
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Old 12-20-2006, 01:19 PM   #9
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Quote:
Originally Posted by Siggie View Post
I own a completely stock 04 Sport 4.L engine with 5 speed. Fuel economy is a sore subject with me. I in no way expect great fuel economy from a Jeep -- If I could get my money back from the purchase, I'd still keep my beloved Jeep -- but it is a sore point.

According to the EPA estimate, my 04 should do 15/19 MPG, city/highway respectively.

My car is well maintained and I drive conservatively with stock road tires and I have consistently done 15MPG maximum in any road condition.

I took the car in to have this subpar performance analyzed and for the 04 the conclusion of the dealer is that ANY condition that would cause poor fuel economy would ALSO result in a fault code being produced. No code, no engine problem. I was advised that 15MPG is actually good for the 04 and that many Jeeps do worse than that. I was also told that there is no aftermarket modification in existence that will improve TJ fuel economy. The mantra was given: If you want fuel economy, don't buy a Jeep.

Anyway, this is just a data point for you. I hope this helps.
I own a 2.5 liter, so this may not be the same result for you big motor guys.

When I bought my '98 TJ used, it was getting 12 mpg. I spent approx. $2000 in tune-up, injection cleaning, minor parts & sizing down to stock tires for city driving. I now get 18 mpg city, regularly. Sometimes that's what it takes

Parts included plugs, plug wires, distributer cap, O2 sensor, brake pads in front (the old ones were literally broken into pieces & some of the pieces might have been dragging), air filter (which I've now replaced with a K&N drop-in), oil change & filter, Lube & complete fluids change, new radiator, & a fan clutch.
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Old 12-20-2006, 01:24 PM   #10
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I don't know about any other brands, but Chevron adds chemicals to their primium grade (91 octane) that they do not add to their 87 octane. In California anyways.

I do agree that using a higher octane gasoline in a motor that does not require one is rarely useful and you waste your money.
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Old 12-20-2006, 01:59 PM   #11
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Quote:
Originally Posted by Jerry Bransford View Post
First, high octane gasolines have no more fuel cleaners than 87 octane does. That's a myth gasoline manufacturers have no interest in dispelling, the same as the false rumor that high octane boosts power in engines not designed for it... totally untrue too. Running high test gasoline not only won't help clean things out, it can also increase the level of deposits because high octane fuel burns slower and may not combust completely, leaving deposits behind. Octane's purpose is to help it resist premature combustion from compression, that is all. And once again, to be sure, the manufacturers do not add additional amounts of fuel injector cleaners to higher-octane fuels.

I have to agree here. Consumer Reports and a couple of those evening news programs have proven this. I'm lucky to get 250 miles out of a tank of gas. Higher grade fuel does nothing. Just another Fleecing Of America.
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Old 12-20-2006, 03:24 PM   #12
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Quote:
Originally Posted by MouthfulOfGrass View Post
I own a 2.5 liter, so this may not be the same result for you big motor guys.

When I bought my '98 TJ used, it was getting 12 mpg. I spent approx. $2000 in tune-up, injection cleaning, minor parts & sizing down to stock tires for city driving. I now get 18 mpg city, regularly. Sometimes that's what it takes

Parts included plugs, plug wires, distributer cap, O2 sensor, brake pads in front (the old ones were literally broken into pieces & some of the pieces might have been dragging), air filter (which I've now replaced with a K&N drop-in), oil change & filter, Lube & complete fluids change, new radiator, & a fan clutch.
Sounds like you've done some good work. If the O2 sensor was bad (the dealer mechanic claims) you'd have a fault code that tells you that it's bad. Mine has no such code. My TJ has 35K miles on it and the ignition components are in tip top shape. Air filter's new (but not a K&N). In any case, an air filter upgrade will have marginal -- very little -- influence on fuel economy. A drag on the wheels by brakes can easily be confirmed by lifting a wheel and turning it by hand -- or if the drag is serious shifting to nuetral and noting the deacceleration. Oil change can give some improvement if the oil is switched from conventional to synthetic (I always use synthetic). Of course, the transaxle and transfer case oils are synthetic (with additives). Basically, the only significant influence on your fuel economy that I can see would have came from the O2 sensor and ignition tune-up (assuming your plugs and wires were worn).

In my case, all these factors are nonissues and I get 15 MPH, driving conservatively with stock tires.
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Old 12-21-2006, 08:07 AM   #13
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O2 sensor

I agree with Jerry, It is probably the O2 sensor. Had a heck of a time with a Grand Cherokee. Every time I pulled my 23' Baja it would foul the O2 sensors.

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