Fuel Vapors

I have a 2001 Windstar. I am smelling stong fuel vapors on the outside and inside near the filler neck. I don't seem to sell them when I have a full tank but when it starts getting under half a tank the fumes start getting stronger.

Sounds like you may have a malfunctioning fuel vapor valve. This would cause fumes to become trapped in the tank and slowly vent out the filler cap instead of passing through the EVAP system. This would very likely cause a fuel vapor smell that would increase as the level of liquid fuel in the tank decreases.

Unfortunately I don't know how to test this valve, the procedure is not described in the shop manual but in the Powertrain Control/Emissions Diagnosis (PC/ED) manual which is a separate document and I don't have it. However pulling the codes would help in confirming this. Other symptoms would include decreased gas mileage and inaccurate fuel gauge reading but the latter can be hard to tell. I believe Winnies are not equipped with a standard fuel sender, the gauge being fed by a vapor pressure sensor instead. A faulty valve should affect the gauge's accuracy but to which point I can't tell.

also check around the fuel cap sealing surface, these develop cracks and leak. you can get a new neck or use a quicksteel weld and work it into the cracks then smooth it out with wet fingers to create a good seal. I did this a year ago and it is still holding