what is the hole in the top of the gas tank for.... i know there is one for the sending unit, one for the filler neck/vent tube... whats the one on top of the tank for?

 

This is for the EEC system (evaporative emission control). There is a check valve that is pressed into a rubber grommet. A line runs from there up to the engine compartment where there is a charcoal canister. The line hooks to the canister and a line runs from there to the air filter housing.
Here is a diagram from the Ford parts catalog. Check item 9B593. This is the valve.
If your truck wasn't equiped with the EEC system the tank didn't have the hole.
Click on the .pdf link to view.

 

yeah the prior tank had a hole drilled out, but the new tank doesnt...

can i plug the tube and run it without... i really dont want to drill on my new tank...

 

Actually, you don't really need to plug the tube. Its only function was to pass the fuel vapor from the tank to the charcoal canister. If its not hooked up to the tank there is nothing flowing through the line.
One thing you MUST DO though is change the fuel filler cap. The one you have is non-vented (the tank vented through the EEC system). Change the cap to a vented one, if you don't you will have fuel starvation issues (at least) or a collapsed fuel tank (at worst).

 

thank you!, thats what i was looking for... your immense knowledge bewilders me!

any particular vented gas cap that would look close to my stock chrome one??

 

figured it out, thanks... this forum is outstanding

 

Looks like some rep points coming your way Mike! Good job!!

 

Well, if you can't dazzle 'em with brilliance then baffle 'em with b*** ***t.
More seriously, thanks. Glad I could help.

Mike

 

Nearly forgot, one other thing. If you look at the two tanks, the nipple for the vent hose next to the filler pipe is located on the opposite side of the filler neck (180 degrees apart). You'll need to get a longer vent hose to "wrap" around the filler neck.