Hey guys, first post here, and first F150 I've owned, had it about a year. It's a 2004 4.6 regular cab.

I went to gas station and the pump kept stopping, almost like the tank is full. I figured problem with the pump and went to another station, same thing. Fuel gauge has been stuck to full since I've had truck, but scanner says 20%.

My first thought was maybe the EVAP canister vent valve, but I am having trouble finding information on where the valve is located and how to replace.

Does anyone have any suggestions as to where I should start to diagnose this? There is no check engine light on, no pending codes or anything. The EVAP monitor is set.

Appreciate any help, need get to work next week and can't add gas. Have tools and experience to fix it, just need help figuring out issue.

 

I think you are correct if the vent valve or the tube from the vent valve closed or blocked it will cause this . I have not worked on it yet. I would also think you should have some codes for a failing evap system test .
The tube out of the cvs must go up in the frame and have some filter end on it, they tell me that can get clogged with mud ,wasp nests etc .
I would crawl under there and remove that vent tube first and see .. Maybe this 03 diagram will help
https://www.f150forum.com/f6/evap-ca...lenoid-382823/

https://www.motor.com/magazine-summa...er-august-2006

 

​​​​​Ok I will go take a look, thanks for the info. It is strange to me no codes, was my first thought. I was just looking at similar diagrams as the ones you sent, I've included them so they may help others. Will update with what i find
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My father's 1979 F-150 had this problem from day one. We never did troubleshoot it and I still don't know what caused it but we found that if we parked on a surface that tilted to the passenger side of the truck that it didn't happen. We found a local gas station that did and we always filled up there whenever possible.

 

The filler neck itself has a vent tube that is supposed to vent out when you are filling up. The evap system does vent the tank, but not when you are filling up. I would check for a blockage there or a pinched hose.

 

I saw mentioned a fuel valve limiter on tank ,can't find anything on it . Something about non serviceable , and valve would also close if truck turned up side down . The carbon canister is high in the frame compared to tank but maybe that valve only lets vapor go to canister. . It really takes someone who has taken one of these tanks down . All of us are just guessing ,been years since I tore open an old metal tank.There is supposed to be a pressure sensor on tank for evap test also . .It is an interesting problem .
this you tube video says there is a screen in the neck

 

Looking at this you tube video i don't see any vent tube in filler neck . I believe the vapors are pushed into the carbon canister as you fill , that would make sense as to not venting to open air for emissons . It could be the rollover valve is in the tank on the neck connection that this guy pointed at . .. I wish he had covered more of each tube and connection as well as the vent on canister not to mention a more detailed closeup of canister. Basically the vapor has to be pushed out as you fill or the back pressure is going to shut gas nozzle off I have heard the canister is very expensive ,he confirmed that I would still confirm the output of the canister is clear including the valve ,it is supposed to be open when denergized ,the pcm only closes it for a vac test on system . Do not energize it for too long it can heat up 2.-3 minutes could be okay or less .
Besides the screen in the neck maybe something is stuck in there .Kids do funny things .

 

I found a bunch of postings on that rollover valve sticking , unfortunately you will have to drop tank to free it up . may have to use your finger . Some guys want to remove it ?