This is the infamous P0455 & P0442 code. I got this error a while back and have been to a local mechanic that replaced the gas cap and canister vent valve. The P0442 code came back on after about 150 miles. I went back to the mechanic which put the truck on the smoke machine but could not find a leak.

I gave up on the local mechanic and turned to a cousin that is a expert mechanic at a local ford dealership. He first flashed the computer and re-ran the test and it failed. He then dropped the fuel tank and pressurized the tank and put snoop (liquid bubble) onto each evap line with no sucess so he gave up pending replacement of each component of the evap system. After talking with the cousin he suggested that when I fill up I should only fill up to 3/4 so that the system goes through more cycles and code will come up faster.

After about 500+ miles and about 40+ startups I decided to start filling up all the way. After approximately two fill-ups the light came back on. I recently put my truck up on jacks and starting vacuum testing individual lines and solenoids. Parts check so far: line from fuel intake to purge solenoid valve, purge solenoid (checked by opening top vent cap and plugging while drawing a vac on bottom port and that allowed gas to pass between both evap ports that attach to bigger diameter lines-one slightly bigger than the other), evap line leaving purge valve to near front most portion of the fuel tank connection.

All have held vacuum, but I did have a little bit of fuel drip from the front portion of the fuel line that runs along the side of the tank. My fuel level in the tank was only about 1/3 full at time of this check. Is it possible that the fuel is getting into this evap line by filling tank to capacity? Is there something that prevent this that need to be replaced? Is it possible that this could have been over looked?

Please help! Sorry for the length of this post. I wanted to be thorough just in case another person can resolve the issue or sould help someone diagnosis this problem. By the way its a 2004 Navigator.

 

I'd like to suggest 3 easy, inexpensive and common solutions to these codes especially as they apply to Fords.
1. Bad gas cap- replace it with an OEM one NOT a cheapo from the local chain parts store.
2. You may be re-filling the tank with the engine running.
3. There may be a blocked vent tube. It would be obvious if the gas pump keeps clicking off as you fill the tank WAY before you are near the FULL mark.

Your mechanic buddy should be able to reset the codes once you try these. If not, disconnect the battery for a minute.

-Good luck!