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Old 11-03-2011, 07:08 PM   #1
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Mileage problems and possible TC issue.

Hey Guys, So I'm having a bit of an issue with the TJ and I'm puzzled.
So I was getting roughly 15.5 MPG. Now I'm getting 11.5.. Here's the story:
She was garaged for a bit, only driven on weekends and really nice nights... my old-lady needed to use a jeep so I figured... fine.. just go easy on her. After her complaining about the mileage I figured she was beating on my jeep so I gave her my liberty and I took the wrangler in order to save it from certain destruction. Well no, I baby it.. always have... and it's getting the 11.5 mpg.
When she went in to get the oil changed, they said it was partially stuck in 4wd(?) and they had to move the transfer case to get it out... I claimed BS.. thinking hell if it was, it'd be undrivable on pavement.. but I can't think of anything else it could be.. It's got a new cat, new oil, changed the plugs, cap, rotor and wires about 10k ago, fresh gas, and I can't notice a difference in how it's driving since before when it was getting the normal mileage.
so 1.) Does that partially stuck in 4wd bit make sense to any of you?
2.) Any help on the mileage?? Could they be related? .. THanks guys!

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Old 11-03-2011, 11:09 PM   #2
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how old are the O2 sensors? Time for replacement?

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Old 11-04-2011, 01:08 AM   #3
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so am i reading it right? you took it to the dealership, they changed the oil and noticed it stuck in 4hi, and they fixed it by moving the t case? does it go in and out of 4x4 now?

o2 sensors is a place to start on mileage. while your under there check for exhaust being bent or clogged. also check that new cat. if it's clogged you would probably have other symptoms but it's worth checking if everything else has been.
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Old 11-04-2011, 03:57 AM   #4
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I don't understand, they moved the transfer case.?
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Old 11-04-2011, 05:28 AM   #5
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Moving the t/c is a load of bunk... 2 things come to mind for your mileage,
1..ethanol, will drop it down to 11 or so mpg, switch to the medium blend.
2.. Remove the throttle body, take all the sensors off, clean everything, reassemble.
I did both, and now get 17 average MPGs
Do that, then if no improvement, check out the O2 sensors.
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Old 11-04-2011, 06:13 AM   #6
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Exactly... all of your reactions were the exact same reaction I had lol... "wtf..."

They didn't fix it... they said somehow, moving the transfer case will fix it... I explained that is not how that shit works, and they went on to inform me that they do this for a living, and instead of getting into a fight I wished them a good day.
It goes in and out of 4wd now fine. They're saying when it's in 2wd, it's still partially stuck in 4wd... I tore up my front yard in 2wd to see if the front wheels leave marks but only the backwheels do... so the front wheels aren't getting any power from the drivetrain so I don't know HOW they say it's partially in 4wd... maybe it's trying to engage the entire time? I don't know.
As far as the sensors go, I haven't pulled any of them. The Jeep has 95k miles on it, and I don't know if any sensors have been replaced at all and if they have, I don't know when... I bought the jeep 2 years ago so my liberty didn't take the brunt of the farm work. But this weekend I can pull the throttle body and check the sensors... see if that does it. I figured a bad or dirty sensor would trigger a CEL, but maybe not.
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Old 11-04-2011, 06:36 AM   #7
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I doubt the tc issue. I'm interested in the o2 idea. Does it throw a code or not?
Do you have hesitation?
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Old 11-04-2011, 08:06 AM   #8
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Makes me wonder if they're not confused because the front driveshaft turns all the time.
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Old 11-04-2011, 08:18 AM   #9
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Slasher, that's exactly what I think too.... I'm not a mechanic.. but I do know how shit works... and I couldn't think of how the 4WD could be partially on, or trying to engage 100% of the time... it's pretty much on or off.
As far as hesitation goes... hmmmm okay, I have 31" tires, on low stock gears. When I start off the line, it's sluggish-ish. But at the same time, it's a jeep, with 31" tires and 13 years old. lol... I wouldn't call it hesitation, but I won't be beating anybody off the line .
Just to throw this in there too... in case it has anything to do with it... I made a post about it a year ago but couldn't get a firm answer.
There is a slight ticking, when it's in gear and given gas. It sounds like a slight exhaust leak... Now this was happening, when i was getting 15.5 mpg... so I'm not sure if it's causing anything... but again, may be related so figured I should mention it.
Like I said, I'm not mechanic lol... I do 99.9% of my own work on the jeep unless my old-lady is driving it on the day that it needs work... then instead of coming home and having me do it for free... she takes it to a place that charges us an arm and a leg... and finds '4wd problems'.... But I can't figure out what it could be.
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Old 11-04-2011, 08:19 AM   #10
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Also there is no CEL... I can get the codes pulled, but I thought if there were codes, there would be a CEL.
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Old 11-04-2011, 08:28 AM   #11
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Quote:
Originally Posted by s14sh3r
Makes me wonder if they're not confused because the front driveshaft turns all the time.
It's a dealership.. I don't trust any of em' BTW,, be sure to use throttle body cleaner and NOT carb cleaner, carb cleaner will damage the electrical components.. I also used a 1/2" soft bristled paint brush to get all the nooks and crannies.. The idle air valve is most likely the culprit, If it is sticking. MPGs will go down.. Be sure to pick up a new throttle body gasket.. It's an easy job, took about 1/2 hour..
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Old 11-04-2011, 08:38 AM   #12
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Quote:
Originally Posted by Rubicondon53

It's a dealership.. I don't trust any of em' BTW,, be sure to use throttle body cleaner and NOT carb cleaner, carb cleaner will damage the electrical components.. I also used a 1/2" soft bristled paint brush to get all the nooks and crannies.. The idle air valve is most likely the culprit, If it is sticking. MPGs will go down.. Be sure to pick up a new throttle body gasket.. It's an easy job, took about 1/2 hour..
I'm curious how does the idle air control have anything to do with fuel mileage? It's used solely for idle, not when you're tooling down the road. He hasn't said anything about a rough idle.
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Old 11-04-2011, 08:42 AM   #13
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I'm curious how does the idle air control have anything to do with fuel mileage? It's used solely for idle, not when you're tooling down the road. He hasn't said anything about a rough idle.
Nope, idle's fine.. I mean it runs fine lol... could POSSIBLY be running a little rich, considering the MPG i'm getting, and sluggishness... but the sluggishness is SOOO subtle, I'm not sure it's even sluggish or a jeep
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Old 11-04-2011, 09:05 AM   #14
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Quote:
Originally Posted by Rubicon2

I'm curious how does the idle air control have anything to do with fuel mileage? It's used solely for idle, not when you're tooling down the road. He hasn't said anything about a rough idle.
I don't know, I had some high idle issues, RPMs wouldn't drop between shifts, etc, I do know, after I cleaned it, my idle issues went away, and my MPGs went back up.. It's an easy fix, and probably needs to be done anyway, and it may fix the problem for $5..,
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96' Lexus 450, locked, loaded and ready to roll..
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Old 11-04-2011, 11:10 AM   #15
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Quote:
Originally Posted by Rubicondon53

I don't know, I had some high idle issues, RPMs wouldn't drop between shifts, etc, I do know, after I cleaned it, my idle issues went away, and my MPGs went back up.. It's an easy fix, and probably needs to be done anyway, and it may fix the problem for $5..,
Hmmm interesting. I've never checked mine and I'm sure now after 6 years and 87,000 miles mine could use a good cleaning.
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Old 11-04-2011, 11:23 AM   #16
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I don't mean to be Capt. Obvious, but, in all of this I haven't heard one mention about the air intake system. I would naturally assume that when you changed everything out (tune-up) that the air filter was also changed, still, have you opened it up to see if it swallowed a load of leaves or something along those lines?

Past that, the cleaning of the intake system and the O2 sensors would be the way to go followed by a verification of correct spark plug gap and ensuring the ignition timing is correct and there is spark to all plugs. Just some thoughts...
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Old 11-04-2011, 12:20 PM   #17
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I don't mean to be Capt. Obvious, but, in all of this I haven't heard one mention about the air intake system. I would naturally assume that when you changed everything out (tune-up) that the air filter was also changed, still, have you opened it up to see if it swallowed a load of leaves or something along those lines?

Past that, the cleaning of the intake system and the O2 sensors would be the way to go followed by a verification of correct spark plug gap and ensuring the ignition timing is correct and there is spark to all plugs. Just some thoughts...
Ahhhh yes I did forget to mention this, sorry. It's got a clean filter, all hoses are clear. Only thing I can think of, is the O2 sensors, but would have liked to see a gradual mileage reduction rather then 15.5 then 10 the next tank lol.
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Old 11-04-2011, 06:50 PM   #18
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what is your idle speed? check for vacuum leak(s)? maybe when changing air filter ect. loosened a hose? a vac. leak will kill your mpg's . just a thought
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Old 11-05-2011, 07:18 AM   #19
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There are a lot if things that can zap mpg and a lot of good suggestions mentioned already.

I have a few other: I had a truck that had a brake problem and found a caliper hanging. Dragging brakes will kill mpg.

Also, my wife recently complained about a Drop in mpg in her Pacifica. I found some leaves blocking the air filter and tire pressure low in all tires. I added about 10 lbs and guess what? No more complaining.

If that were my jeep I would pull the plugs and inspect for running rich. I would use a good quality fuel injection cleaner. Probably seafoam it. I would also try a fuel with no ethanol. And I would check the brakes.
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Old 11-05-2011, 09:36 AM   #20
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Btw, an exhaust leak can cause major problems with the O2 sensor resulting in the car to dump more fuel.
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Old 11-06-2011, 06:16 AM   #21
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Btw, an exhaust leak can cause major problems with the O2 sensor resulting in the car to dump more fuel.

That was what was wrong with my 97. I just bought it a couple of weeks ago and the manifold was cracked. I also noticed really crappy MPG so I went ahead and replaced the manifold. Two days ago I am thinking everything is fine when my check engine light comes on. Found out it was the upstream oxygen sensor. I think that since the exhaust manifold was leaking the oxygen sensor wasn't getting picked up as bad and since I fixed the leak the next item to go was the O2 sensor.

60 bucks and 10 minutes later that is fixed but I haven't been able to see if it makes a difference in my mpg's but I sure hope it does.

I think if you have over 80K-100K miles you should just replace the O2 sensor. It is cheap, easy and something you can take out of the equation in order to troubleshoot further. I will report back after I get a chance to run a full tank to see if my mpg's does improve. I have read on here that just because you do not have a CEL on doesn't mean the O2 isn't bad.....in my case it might have been bad but because of the cracked manifold it wasn't getting picked up.

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