The Real Fix
The issue of gas "burping" out of the filler neck right after the pump clicks off when the tank is full is a fairly common issue among Jeep Wrangler TJs. The cause of this is the ethanol in the gas causing plastic parts in the Inlet Check Valve (ICV) to bind and not close quickly enough to prevent fuel back-splash when full.
Owners of 2005 - 2006 TJ Wranglers were left up shit creek by Chrysler and the NHTSA on this one. '07 and newer got a warranty extension (NHTSA closed the investigation taking the heat off Chrysler) '05-'06 owners got the shaft. There's almost no point I filing a complaint with NHTSA any more because our complaints were already dismissed as "Internet hype".
Using the GM hose to address the "fuel spit back" problem is a hack (see below for the "hack" fix). This technique was first posted in the Internet many years ago and has made the rounds enough times in the jeep forums that it has become permanently embedded in the collective knowledge base and won't go away.
The problem is caused by a sticking plastic overflow valve at the inlet to the fuel tank.
The actual fix is is to drop the tank, sand the nubs on the plastic piece in the overflow valve , reassemble the valve then raise the tank back in place. The only "part" required is a piece of sandpaper as shown in the video below.
The Temporary Fix
This is the original "fix" for the fuel spit back problem. While it will usually fix the problem, it is a band-aid at best, and should only be thought of as a temporary fix, whereas the above method is the actual long term fix.
This is how GM fixed the exact same problem in the Trailblazers, Envoys, Bravadas, etc.
Amazon has the replacement part for around $30 here:
http://www.amazon.com/gp/product/B00GUCRISO/?tag=wranglerorg-20
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The bulge in the middle is a little flapper valve:
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Here's our lower hose that connects the filler tube to the tank:
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Here's a how to guide:
The inside diameters are identical. Cut 1 1/4"off the small end and 1 3/4" off the big end. I started out only cutting about 3/4" from the small end to make it the same length as our hose, but it can't make the bend without kinking. I cut some more off and it made for less of a bend and no kink.
If you have a body lift, you'll probably need to cut less off. Start small, you can always cut more but once you cut it too short you're on your own...:
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Swap your old clamps onto the GM part:
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The lower clamp has a little clip on it that you put at the top of the hose so you can feel that it's oriented right when you put in on the tank. The round notch on the GM hoseis there to align it with its intended tank, use it as a reference for installing the Jeep clamp.
This is very important when it comes to re-installing the new hose. You'll have to feel for this clip because you won't be able to see it clearly:
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That's it!
Reinstall and you're done. I had to remove the 4 torx screws attaching the filler neck to the body to get the new hose on it. I didn't have to disconnect any other lines or take it completely out, but just needed to move the neck around to get the new hose on.
Removal and istallation on a TJ is extremely simple.
Access through lower wheel well cover:
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Loosen the 2 hose clampsand remove the original rubber hose. (1/4" screw clamp upper & 5/16" screw clamp lower) I found it easier to remove the stock hose with the upper filler neck still attached to the body so I could pull down on it.
Cut GM hoseand swap Jeep clamps over (see previous posts).
Remove the 4 torxscrews attaching upper filler pipe to body. You don't have to remove the pipe completely. I didn't even disconnect the tank vent, axle vent, and locker pump lines. You'll only need to move and twist it around a bit to get the new hose on:
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Install modified GM hose, tighten all fasteners, replace trim pieces as necessary - you're done!!!
Note: Make sure the hose is oriented correctly. If the flapper sits crooked or upside down it won't work right. The round notch on the big end of the GM hose before cutting it is for orienting it to its intended tank. You'll have to feel for the little clip on the Jeep hose clamp and make sure it sits at 12 o'clock on the tank inlet.
Here's the installed hose:
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