Gas wont go down filler neck

CBurt98

New Member
Apr 12, 2022
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Kentucky
Hi all,
I have a 2001 Mustang GT and just recently replaced the fuel pump, filler neck grommet, and filler neck. The issue i'm having is after installing these when I try to fill the tank with gas; gas will fill all the way to the top of the filler neck and I have to wait several seconds for it to trickle down into the tank. I removed the tank, again, and the filler neck will allow gas to flow freely when tested while it was disassembled.

I've also tried unhooking all the evap/vent lines to see if the charcoal can or venting was the culprit after reading wmburns thread. I am able to blow through the lines but the filler neck would still fill up with gas when assembled with the tank.

Thanks in advance for any advice!
 
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manicmechanic007

5 Year Member
Sep 26, 2017
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If you just replaced all that the tube must be kinked or out of position?
By chance a plug was left on the aspirator or vent tube?
Is it a Ford part? Maybe the cheap arse china anti siphon is whack? Loose that maybe
Pull it the F back out and test it with water
 

CBurt98

New Member
Apr 12, 2022
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Kentucky
@manicmechanic007 @hotpony I've just recently replaced all the evap lines with thick, rubber fuel line that's too heavy to be kinked in the install. The filler neck and anti siphon both worked out of the car with water.
After i reassembled everything and didn't completely button up the tank and made sure all the hoses were free I still have the same issue.

Does the fuel vapor valve have anything to do with the air while filling or is it just for trapped fumes after its already full?

Thanks
 
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weendoggy

Active Member
Jan 14, 2019
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If you can remove the vent valve on top and see if fuel will go in, you've pretty much found the issue of air being trapped. Why? Not sure, but a new valve (plastic) may be the issue. Did you have this before?

If you've had the tank out, with the pump in, fuel vent valve in, and filler neck in (as it would be in the car), does it do the same thing? If so, easy to diagnose before installing again.
 

manicmechanic007

5 Year Member
Sep 26, 2017
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Both I believe
It is both a vent and anti roll over valve (inadequate to vent the tank for fuel fill though) There is the evap valve and canister purge valve on the other side
Your tank air is designed to go back up the fill pipe thru the 1/2 inch hose
Maybe try sucking on that pipe to be sure air goes thru to the tank okay
 

CBurt98

New Member
Apr 12, 2022
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Kentucky
@manicmechanic007 There's a larger hose that runs beside the filler neck and out to open air that's also connected to the charcoal can. Then a smaller one that routes into the actual filler neck towards the top and connects to the lines that go to the vapor valve, fuel tank pressure sensor, charcoal can again, and to the front of the car. Any idea which one is for venting air from the tank?

Thanks for answering these questions
 

manicmechanic007

5 Year Member
Sep 26, 2017
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None of the evap vapor hoses are designed to vent the tank for fuel fill
Just the filler neck
All the rest although hooked up, have valves on the other side
The air is designed to come back up the filler neck and out around the fill nozzle
If you put a 5 foot hose on that tube on the filler neck and tried to fill the tank what happens?
Need to make sure air comes rushing out that little pipe as fuel goes in
You replaced your oem fill pipe for what reason?
You may need to modify the one you have (remove the anti siphon ball) (or crush it at least)
 

hotpony

Founding Member
Feb 26, 1999
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The rollover vent in my car was my issue, I have an 03 Cobra tank in a 96 Cobra but I got the blue rollover vent (2003 Ford Mustang Fuel Tank Vapor Vent Check Valve Ford OEM F8DZ-9B593-AB) and hollowed it out, then the tube I connected to a vent filter like for a boat. I don't have a charcoal canister in my car though and my pressure issues went away, it was also starving the engine for fuel under boost too when the demand was high because it could not equalize pressure so it was basically creating a vacuum in the tank.