Gas mileage fluctuation -
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Unread 02-25-2009, 08:43 PM   #1
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Join Date: Nov 2008
Location: Central NY
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Gas mileage fluctuation

My gas mileage has fluctuated quite a lot lately: After a 200 mile round trip staying at around 55-60 on rt 20, I got 22 mpg, and when I filled up today I got a mediocre 12.5 mpg after 120 miles of around town driving. Now I know the 4.0 isn't a gas sipper, but this seems pretty low for a stock wrangler. Is this kind of fluctuation normal? I have heard people speak of staying in open loop or something during short around town trips (usual drives are about 4 miles), could this be my problem? I know I need to replace my O2 sensor, and possibly my CPS (CEL comes on after ~15 miles, then goes off). I have searched the forum and know that different wranglers can get very different mileage, just wondering why it seems to fluctuate so much, I am a very conservative driver.

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Unread 02-25-2009, 08:45 PM   #2
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sittin in traffic KILLS MPG, doubt your o2 sensor has anything to do with it as i'm runni w/ no cat and gettin better than you are, what gear do you run in around town? i tend to shift very early (like around 1000) but thats with 33's also.
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Unread 02-25-2009, 09:08 PM   #3
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1991 YJ Wrangler 
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Are you buying gas at the same station every time? Some stations have ****ty gas. I easily get 200-250 miles a tank. Last week I filled up at a station I have never been to and got less than 200 highway miles in that tank. Went back to one of my normal gas stations and my mileage is back where it was.
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Unread 02-25-2009, 09:40 PM   #4
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If your O2 sensor is really shot than replacing it would give you better mileage. The CPS could also lead to lower mileage. I dont think either of these are the specific problem in this case though. I think its just going from all highway to driving in city. I usually get ~20mpg mixed, but when I only do city it drops to ~16.
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Unread 02-25-2009, 09:48 PM   #5
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Location: Syracuse, NY
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Knowing where you are driving tells me alot. It is simply the city/highway issue. AND around here, some gas stations can kill your mileage and some are excellent. IT also has to do with the temp outside. I get crappy mileage when it is cold.

My other suggestion is to check your engine codes.

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