Gas Tank Leaking?? How to Drop your Fuel Tank / Replace the Filler Neck Gasket - Forums at Modded Mustangs
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post #1 of 71 Old September 12th, 2008, 06:12 PM Thread Starter
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Post Gas Tank Leaking?? How to Drop your Fuel Tank / Replace the Filler Neck Gasket

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My gas tank started leaking a few weeks ago, only on the right side when the car was on an incline to the left, and only when there was a decent amount of gas in the tank (I noticed it when I was filling it up). After considerable research online, I figured out that the filler neck gasket had gone bad, which apparently is a common problem with '99-'04 Mustangs. So, I started on my quest to fix it.

The first task was to figure out how to drop the gas tank. I've never done this before on my car, but after some googling on the interweb I found a couple sites with instructions on how to do it. Seemed like a pretty easy task, just a b@#$% to do. Definitely helps if you have a buddy to help drop it. I was able to do it myself.

Once dropped, I was able to confirm that the gasket had gone bad. It was in two pieces, with one half just hanging around the filler neck loosely, and the other dropped somewhere inside of the tank. That sent me on a quick trip to the local Ford dealership to buy the new part, which was $17 with my military discount. (About $19 regular price) They should have it in stock, but I would call beforehand.

So, I figured that for once I would document the endeavor that was fixing my leaky gas tank with pictures and a MM thread (hopefully sticky). Here goes.




Here's the car jacked up and ready to go. I would highly recommend using jack stands for this operation, as you'll need quite a bit of space to drop the tank. A lift would be even better, but I haven't quite installed that in my garage yet.



You'll need to do a few things first before dropping the tank. I read online that its always a good idea to disconnect the fuel cutoff switch, so I did that. It's located in the trunk.






Disconnect the battery for sure. Don't want power running to anything. Then make sure you bleed off the fuel pressure in the engine compartment from the fuel rail:






After that, you'll need to remove three bolts in order to lower the tank. There are two metal straps that hold the tank up; one comes off completely (right side looking at the back of the car) and the other has one bolt and swings freely from its other end (left side of the tank). Notice the fuel filter in the first picture, I'll touch on that in a little bit.












After you loosen and remove the three bolts, you should be able to lower the tank. Definitely have a jack or something underneath the tank to gently lower it down.







It's hard to get the filler neck completely out of the tank. You'll need to disconnect all lines before trying to pull it out. Here's the part where you'll need to run to Advance Auto or NAPA unless you were smart and read this all the way through before starting. You need a fuel line disconnect tool in order to get the line disconnected from the tank. MAKE SURE you don't try and use some other tool (i.e. screwdriver and a hammer) to try and disconnect it; you might end up having to replace the fuel line. I believe the line is 5/16"; buy the right size tool accordingly. It was about $6 at Advance Auto for me.





There are a few other hoses you'll need to disconnect, notably up by the filler neck near the location of the gas cap. You don't have to disconnect everything; just enough so that you can set the tank on the floor. Once you're able to do that, I removed the fuel pump because half of the gasket had dropped inside of the tank. It was pretty hard to fish it out of there but definitely something you don't want to leave in there.





Here's the end of the filler neck once the tank was dropped. On the end of it there is a little plastic piece that clips onto it; I found it inside the tank. It might come off when you pull the tank out, make sure you look inside the tank and clip it back on.






Here's what the old gasket looked like:










Here's the part number of the gasket. If you don't remember to bring it to the Ford dealership they should still be able to hook you up as long as you tell them what you need.









Here's the new gasket installed on the tank. I read a post online where someone recommended putting Vaseline on the gasket to help get it on, but I just got it a little wet with some gas inside the tank and it went on fine, with a little bit of help from a small flat-headed screw driver. Before you put everything back together, I would recommend using this opportunity to replace the fuel filter, as you'll already have all the tools you need out (plus the fuel line disconnect tool) and PLENTY of space to do it.






After that, install everything back together. Remember when you go to start the car, to reconnect the battery and fuel disconnect switch first, then turn the key to ON for a few seconds to let the fuel pressure build up. The car should start up.

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post #2 of 71 Old September 12th, 2008, 06:17 PM Thread Starter
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Additional Pics

Here's an additional pic of the filler neck partially inside the tank, this is where I was still disconnecting lines in order to get enough wiggle room to get the tank to pull out all the way. If you look behind the filler neck tube you can see the two other lines you need to disconnect from the gas cap feed. Also shows one half of the old gasket loosely hanging there.


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post #3 of 71 Old September 12th, 2008, 06:32 PM
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Ah yes. That gasket leaks ALL the time. We sell a bunch of those. Nice write-up!


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post #4 of 71 Old September 12th, 2008, 06:52 PM
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i think thats what mine has, it stinks like gas after i drove hard or when i feel the tank all the way but there is something weird that when im fueling my car it wont stop by itself when it filled up, it would just lick after the tank had been filled up
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post #5 of 71 Old September 12th, 2008, 07:38 PM
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nice write-up bro...

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post #6 of 71 Old September 12th, 2008, 07:53 PM
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post #7 of 71 Old September 12th, 2008, 07:54 PM
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Good info. Thanks.
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post #8 of 71 Old September 15th, 2008, 03:03 PM Thread Starter
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I'm hoping this can become a sticky because I did a lot of research before figuring out how to do all this.

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post #9 of 71 Old September 15th, 2008, 03:23 PM
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Very informative!

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post #10 of 71 Old September 15th, 2008, 03:55 PM
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nice job. great sticky material.

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post #11 of 71 Old September 15th, 2008, 04:21 PM
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YES. AWSEOME write dude. I think even the most novice mechanics could figure it out. Very detailed man.

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post #12 of 71 Old September 15th, 2008, 09:22 PM
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i dont understand why you dropped the tank,
i've changed mine last year without dropping the tank, it was a ~30minutes job...
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post #13 of 71 Old September 15th, 2008, 09:26 PM
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very good write up!
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post #14 of 71 Old September 18th, 2008, 10:28 PM
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I just did mine today and no more gas smell
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post #15 of 71 Old September 18th, 2008, 10:31 PM Thread Starter
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Quote:
Originally Posted by Ace_Cobra View Post
i dont understand why you dropped the tank,
i've changed mine last year without dropping the tank, it was a ~30minutes job...
In my research, I had also read that you can do this without dropping the tank, but that is makes it a lot harder when you don't. Plus, this is a great oppurtunity to replace the fuel filter.

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post #16 of 71 Old September 19th, 2008, 07:26 AM
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yeah thats an easy fix, when i was at the ford house i had a Gt with evap codes and found that to be the problem

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post #17 of 71 Old September 19th, 2008, 08:59 AM
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Nice write up. I was the one who used vaseline. Some points to add:

1. Make sure you are real careful with the filler neck, you don't want to break it.
2. I disconnected all lines and the fuel line before I dropped the tank....made it a bit easier to manage.
3. Be extra careful when relieving the pressure at the rail. I used a big rag to soak up all the gas coming out. The manual says to run the car with the Fuel C/O switch disconnected till it stalls out. I did this then relieved the extra pressure at the rails.

Very nice write up. Good lookin car to!

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post #18 of 71 Old September 19th, 2008, 09:44 AM
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Nice write up. This is also a good double for replacing the fuel pump with a few extra steps to take the fuel pump assembly out of the tank. If you have the tank dropped already it'd be a good time to clean up the fuel pump assembly especially if that gasket has been ripped or torn. I know when I replaced the fuel pump on my old Bullitt for the blower setup there was a lot of crap in the botom of the fuel pump assembly.

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post #19 of 71 Old September 19th, 2008, 04:05 PM
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Great Job. I changed mine last night because it leaked after a fuel pump swap. This writeup made the job easy. Mine didn't split completely in half so I didn't have to pull the pump. The gasket cost me $26 out here in Cali. Thanks!!
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post #20 of 71 Old September 19th, 2008, 04:13 PM Thread Starter
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Quote:
Originally Posted by smccoy916 View Post
Great Job. I changed mine last night because it leaked after a fuel pump swap. This writeup made the job easy. Mine didn't split completely in half so I didn't have to pull the pump. The gasket cost me $26 out here in Cali. Thanks!!
No problem. Glad to hear its helping others. Hopefully this can become a sticky.

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