I am the original owner of a 2003 GT convertible, I'm on disability so believe it or not the car only has 65,000 original miles on it since it's lightly driven. I've had three tops on it and unbelievably I'm on my fourth fuel pump replacement (all were oem replacements by a Ford dealership except the last one). My dilemma is; after the last replacement the fuel cap light came on, the mechanic replaced the cap twice, ran a smoke check and couldn't find any leak or pressure change. After the fuel door light is on for a bit the service engine soon comes on. The mechanic (shop owner) said the code indicated a fuel door/cap leak. This has happened twice now in the last month and I'm getting annoyed seeing these yellow warning lights. I should also mention that after the mechanic resets the warning system and I fill the tank full the lights stay off but when the tank gets down to 3/4 full the lights come on. Anyone got any ideas because the manager said he's stumped.

 

There's a fuel vapor recovery canister on the drivers side of the fuel tank. It's equipped with a purge valve that's sealed to the canister using "O" rings.
Also, vapor lines to the tank can be suspect.
I recently replaced all of these "O" rings as well as the purge valve and reset the light on my '04.

 

Thanks for the reply. Would the mechanic see smoke coming from the recovery canister, connections or hoses when he was doing a smoke and pressure test?

 

Good point. I've never done a smoke test, but things can get missed.
Another area could be the filler neck. There's a gasket at the tank that may seal up OK when submerged in fuel, but leak air once the level drops.
I went ahead and replaced this along with the filler neck.
Check these guys out:
http://www.fillernecksupply.com/
I've bought two filler necks (one for my truck) from this site and have been very pleased.