Fuel filler neck flapper stuck open - Ford Mustang Forum
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post #1 of 8 (permalink) Old 05-19-2018 Thread Starter
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Fuel filler neck flapper stuck open

Ok guys. Does anyone have a temporary fix for a stuck fuel filler neck flapper? Check Gas Cap light came on and I have a brand new gas cap on, rubber seal is good. No leaks in the filler neck and grommet looks good. Not leaking fuel either. Any information would be helpful.

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post #2 of 8 (permalink) Old 05-20-2018
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I give up. What model year Mustang are we talking about?

Further what is the exact DTC code? There are 1,000's of DTC codes and they each have a story to tell.

This is a very different problem if we are talking about a 1996-2004 model year verses a 2005+ model year.

If this car is a 1996-2004 model year then stuck flapper isn't causing the problem. There's likely a leak somewhere else in the EVAP system. More trouble shooting is needed.

If this car is a 2005+ model year with the capless fuel filler there is a procedure to un-stick the flapper and reseal the gas vapor system. Here's a youtube link to a "how to" from a great source fordtechmakuloco.


Ford Quick Tips: #4 Ford Capless Fuel Filler Maintenance



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post #3 of 8 (permalink) Old 05-20-2018 Thread Starter
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2003. The code was I believe p0455. EVAP Leak code.
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post #4 of 8 (permalink) Old 05-20-2018
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Check for a vacuum line cracked or disconnected.
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post #5 of 8 (permalink) Old 05-21-2018 Thread Starter
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I will check that out. Thanks
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post #6 of 8 (permalink) Old 06-09-2018
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For older Mustangs with EVAP leaks also check:
  • For a rusted out filler neck. Especially under the plastic rock shield (if present).
  • Dry rotted gas tank filler neck grommet.

Gas vapors are very hard on rubber parts. +1 on checking for dry rotted vacuum lines in the engine bay.

IMO the stuck open flapper valve is not causing the DTC code.

More information about the gas tank filler neck grommet.
https://www.allfordmustangs.com/forum...tank-help.html

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post #7 of 8 (permalink) Old 06-09-2018
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Stuck flapper indicates nothing more than the presence of corrosion on pre 2005 Mustangs, means the same and will probably not throw any codes in the newer ones. If that area is corroded, then the rest of the pipe is probably messed up real nasty.

It's an anti-siphoning spring loaded thingy with a sharp edge that will capture non-metallic or fluted metal hoses in the pipe and will block garden hoses from getting in at all.

It will also stop you from removing a gas can with a plastic filler neck. Don't ask me how I know that.

You only need a flat blade screwdriver to push the flapper door out of the plastic hose attached to the gas can.

1:00 AM January 28th 1974, 23 deg F median of I-495 AKA Washington Beltway, 1973 Karmann-Ghia out of gas (hers). Round trip walk of 1/2 mile to the nearest exit and a flat blade screwdriver got me and my Fiance out of trouble. Very COLD walk, very WARM warm up later. A very good night. All's well that ends well. VERY well.

I told you not to ask, didn't I?
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post #8 of 8 (permalink) Old 06-23-2018 Thread Starter
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You were correct wmburns. EVAP leak was coming from dry rotted grommet. I swapped grommet and fuel pump and sending unit. Old sending unit arm was stuck and would not move freely. All codes are gone, no more CEL. Have a new problem now though. This car is killing me lol.
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