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Unread 04-02-2009, 10:48 PM   #1
dmolaver15
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2004 WJ 
 
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how much can an evap leak affect gas milage?

i keep getting error code p0442, medium evap system leak, and not only is the little orange light on the dash starting to drive me crazy, but i'm starting to wonder if it's adding to my already horrific gas milage. Now before you get all cranky about complaining about gas milage in a lifted jeep.. i'm only getting 8.5mpg on a light foot, given i have 33" at's and a 5" lift, that still doesn't seem right compared to around 13 on 4" and 31" mt's..

so the code: p0442, the ever resourceful wjjeeps claims that my gas cap may be the cause of this, and it took a brand new gas cap to prove that theory incorrect. wjjeeps also offers a link to a chrysler Tech. Service Bulletin (TSB). The TSB claims that it only pertains to the year 2002 jeep wj, mine is a 2004 however. The TSB is highlighting issues with a bad LDP vent valve. I don't have any idea what the heck that is, but i'm thinking it might be my problem!

I'm leading myself to believe that the LDP vent valve is part of the weird network of tubing behind my rear driver side wheel, that has been exposed to both on and off road conditions for about 5 months now, since my rear bumper has kicked the bucket. Am i going on the right track with this, or should i be looking in another direction as to fixing the problem? Was i correct about this problem affecting my gas milage? If i'm not right about the LDP valve being under the bumper, where should i be looking to next to track down what is causing this evap. system leak?

thanks in advance, i know that was a mouthful, but i really need to get this thing worked out!

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Unread 04-02-2009, 11:17 PM   #2
Kruzin
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An A/C evap leak should not affect your MPG at all.
33s (with poor gearing) and 5" lift (with it's poor aerodynamics), could easily add up to <9mpg.
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Unread 04-03-2009, 05:42 AM   #3
Marcos
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He's talking about an evaporative emissions (fuel vapor) control leak, not A/C evaporator core.
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Unread 04-03-2009, 09:06 AM   #4
ZJcrawler45
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i busted mine and all the rubber pellets fell out. I just chopped all the hoses off and connected them with a "T". Never got any codes though. As far as gas mileage i never noticed a difference.
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Unread 04-03-2009, 09:12 AM   #5
walter_da_jpr
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I think it can negatively effect your mileage.
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Unread 04-03-2009, 12:25 PM   #6
dmolaver15
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bump anyone?
was i right about the thing under where my bumper goes being the LDP valve?
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Unread 04-03-2009, 03:59 PM   #7
ratmonkey
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check the evap canister area for vac leaks/disconnected lines/cracks. (that thingy in the back) yes, i can cause a serious drop in mileage. though a 4.0 with 33's on stock gears probably won't get you better than 10 around town if you're lucky and accelerate like a turtle.
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Unread 04-03-2009, 04:06 PM   #8
CaribouLouWJ
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I have the same code.
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Unread 04-03-2009, 09:11 PM   #9
blu_wj
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I had the same code for a while and I found one cracked hose so I replaced it and that didn't fix it. My problem was the lock nut for the fuel pump some how rattled loose so I tightened it and no more code. But do check all your evap lines. There is a diagram on the inside of your hood. Number one thing from what I have heard would be the evap charcoal canister. Your evap system pressurizes your fuel tank to get all fumes out and routes them to your charcoal canister then routes the fumes to the intake manifold to be burnt I believe.
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Unread 04-03-2009, 10:28 PM   #10
dmolaver15
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Quote:
Originally Posted by blu_wj View Post
I had the same code for a while and I found one cracked hose so I replaced it and that didn't fix it. My problem was the lock nut for the fuel pump some how rattled loose so I tightened it and no more code. But do check all your evap lines. There is a diagram on the inside of your hood. Number one thing from what I have heard would be the evap charcoal canister. Your evap system pressurizes your fuel tank to get all fumes out and routes them to your charcoal canister then routes the fumes to the intake manifold to be burnt I believe.
and the charcoal canister is the thing under wherre my rear bumper would be? or is it upfront?
also where is the diagram underneath the hood? is it under the lining on the hood itself?
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Unread 04-04-2009, 05:37 AM   #11
ratmonkey
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it's under the front bumper on zj's and inside the rear wheel well on wj's. good luck tracing all those lines out.
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Unread 04-04-2009, 08:27 AM   #12
4jeepers
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Quote:
Originally Posted by ratmonkey View Post
it's under the front bumper on zj's and inside the rear wheel well on wj's. good luck tracing all those lines out.
I agree VERY good luck tracing all those lines out! However with a lot of patience and ten bruised knuckles you will find the problem! If that is the problem!
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Unread 04-04-2009, 04:05 PM   #13
blu_wj
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the diagram should be near the hood striker latch. There is a access panel for the evap canister in the driver side rear wheel well and held with 4 plastic rivets. It would be better to take off the bumper though because you can see the whole setup.
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Unread 04-09-2009, 10:57 PM   #14
dmolaver15
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so, i seem to have fixed the evap. leak. i tightened all the evap lines around hte gas tank when i did the tank lift a couple days ago. since then my gas milage has gone up to about 10.5 per gallon.
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6.5" IRO Front and Rear Longarms
Soft 8's, 285/75/16 BFG Mall Terrains
Super 44 with 3" Side Dump
Dana 44a, 4.56's

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Unread 07-19-2009, 09:33 PM   #15
koolaid5
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I'm have the same problem with my TJ. Can someone take a pic of where the evap lines I need to check are?
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