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Ok I have been getting about 18.3 mpg's after all my mods but the last few tanks i have been averaging 12.6!! I took it to the dealership(i needed a oil change anywho and was lazy) so i had them check it and they said nothing was wrong with her. I use mostly premium fuel. My mods are, 3 inch lift, 185 nitto's, throttle spacer, winch and lucrum mount, allpro air dam and lights, shorty headers, plus some sound stuff. But they have all been there for a while. My check engine light plus 3 others keep coming on and off but every time i go to get it read its off by the time i get there! anyone else had this problem? :mecry:
 

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Ok I have been getting about 18.3 mpg's after all my mods but the last few tanks i have been averaging 12.6!! I took it to the dealership(i needed a oil change anywho and was lazy) so i had them check it and they said nothing was wrong with her. I use mostly premium fuel. My mods are, 3 inch lift, 185 nitto's, throttle spacer, winch and lucrum mount, allpro air dam and lights, shorty headers, plus some sound stuff. But they have all been there for a while. My check engine light plus 3 others keep coming on and off but every time i go to get it read its off by the time i get there! anyone else had this problem? :mecry:

Odd problem..


I see that mileage sometimes but i also have a lead foot and leg.




I did not see it mentioned but do you have a CAI?? If so, you may want to check the rubber couplings, make sure they have not come disconnected to the point where you are sucking in only warm air.

If not, check your stock intake fittings.. something might be disconnected. Check to see if the MAF (mass airflow sensor) is connected tightley.

Open the hood and start grabbing stuff.. look for any lose fittings anywhere.
 

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yeah, with that set-up you should get about an all around average of 17-18. Sometimes i get 19 close to 20 on the highway. Something is wrong, but i have no idea.
 

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I've got the same thing w/o check engine light but have noticed my Automatic sometimes shifting hard & or erratic.

Do have CAI & will check it out.
 

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maybe check your tire pressure and intake filter, but i have also heard that when it gets towards summer they start mixing ethanol into the gas in some states, which can effect your mileage.
 

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Check The Sensors And Make Sure They Are Clean And Tight
 

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Depending on mileage, the spark plugs might need to be replaced? My buddy replaced his at like 17000 miles and they were covered with carbon. Have you been using the same station to fill up? I've noticed differences in mileage using BP and Quiktrip gas. Weather could definitely be a factor as well. Premium peaked at $4.19 a gallon around here at some stations, it hurts :(. Hope you get it sorted out. The check engine lights could have something to do with your O2 sensors, maybe they need to be cleaned?
 

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Discussion Starter #9
i will check my sensors and fittings and maf today. I know my tire pressor is good. I guess I have been waiting for an excuse to go buy new spark plugs so I will do that and report. I dont have a CAI yet but its on the list after rock rails lol. Thanks all
 

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Could be 02 sensor. I'd advise doing one thing at a time. If you do 3-4 and mileage gets better then you'll wonder which one of the 3-4 things you did was the fix. :thinkerg:
 

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18.3 mpg with those mods? Is that all highway, because I don't get that mileage around town, and I'm stock. As for the warning light coming on, get a scanguage to find out what they're about.
 

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18.3 mpg with those mods? Is that all highway, because I don't get that mileage around town, and I'm stock. As for the warning light coming on, get a scanguage to find out what they're about.
Scan gauge is on my list and yes that is my average around town / highwa driving i do about 60 %around town 40 %highway.
 

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My check engine light plus 3 others keep coming on and off but every time i go to get it read its off by the time i get there!
The computer should save at least the last three codes even if the light goes off; the dealer (or anyone else) can read them with an OBD-II scanner no matter if the light is still on or not.
 

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The check engine light may, or may not be directly related to the low mileage issue. All of the above suggestions are real possibilities, but it's a hit or miss thing and that can be an expensive, time consuming way to fix a problem. It's much better to pinpoint the problem first. As 1911 said, the computer should have the codes saved. Take it to any auto parts place and they can do a scan for you normally at no charge.

I've dipped down into the same very low mileage range on occasion. Short trips at low speed around town can seriously affect mileage. I get much better mileage at highway speeds vs. putting around at 25-35 with frequent stops and traffic lights. A/C on also hurts mileage. I don't have a lot of high drag mods, so that's not it. I tend to let 'er rip now and then which makes the FJ gulp gas, but most of the time I soft pedal it.

I second the Scangauge II. I don't have one yet, but it's high on my list. The Scanguage will show your mpg on the fly among other things.
 

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if you get it narrowed down to any particular item let us know what it was
 

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Check all the air tube connections on the CAI and make sure the MAF plug is connected tight. Also, I would check to make sure your O2 sensors are connected properly (you stated you have headers). For your mileage to drop this much, this quickly you likely have a sensor that is getting an intermittent signal or no signal at all. Since the MIL is coming on and going off it sounds like a loose connection. The sensors that affect fuel mapping most are the MAF, O2 and engine temp sensors.

DEWFPO
 

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Ok I have been getting about 18.3 mpg's after all my mods but the last few tanks i have been averaging 12.6!! I took it to the dealership(i needed a oil change anywho and was lazy) so i had them check it and they said nothing was wrong with her. I use mostly premium fuel. My mods are, 3 inch lift, 185 nitto's, throttle spacer, winch and lucrum mount, allpro air dam and lights, shorty headers, plus some sound stuff. But they have all been there for a while. My check engine light plus 3 others keep coming on and off but every time i go to get it read its off by the time i get there! anyone else had this problem? :mecry:


Take the Positive side off the batt and leave it off for about 2 hours and then plug it all back in. This will reset the Computer back to the factory settings.. About a tank later you will notice vast improvments..
This happened to mine a few months ago and I have now gone back up to what I was previously getting...
Hope this helps...

:cheers:
 

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oh my gosh Ive had the same problem! granted I have a 6" lift and 35" tires but I was getting 12-13 miles per gallon, then all of a sudden one week it dropped to 9 miles per gallon and my check engine light came on...

Ive been meaning to go to the dealership to get it checked but A) i'm extremely busy B) I know they are going to say its my mods...but I was getting 12-13 mpg after my mods, then it dropped to 9ish...

let me know if you figure it out
 

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engine light on and off tells me you have an o2 sensor or sensors flaking out, thus causing the computor to keep flaking.. i bet if you have them check those or maybe you need to check the connections that they plug into you might find something hope this helps:bandit:
 

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engine light on and off tells me you have an o2 sensor or sensors flaking out, thus causing the computor to keep flaking.. i bet if you have them check those or maybe you need to check the connections that they plug into you might find something hope this helps:bandit:
Since the check engine light system monitors 50 plus different parameters how does this tell you its for sure the O2 sensors? Telepathy??

I agree the check engine light on is pointing to something likely pertinent in his case, just throwing expensive parts at the issue isn't prudent.
 
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