geesh stop yelling! hahah
most trucks do not have the gas cap light, only 96+ OBD-II trucks and not even all of those.
There are two fuel systems the return style and the non return style.
His 94 truck has a canister purge solenoid which is opened and closed by the trucks computer. When the valve opens the vapor line and charcoal canister are purged of any collected vapors from the top of the gas tank, I believe the valve opens at WOT only. The valve is connected to the throttle body on the OHV 4.0L so the vapors are mixed with the incoming air and burned up in the combustion chambers.
the 96+ trucks have the same basic system, but they actually have two solenoids, one is mounted up front under the battery tray and the second is mounted back above the spare tire, where the charcoal canister also resides.
On either of these EVAC systems if the canister purge solenoid is stuck open, the throttle body (manifold vacuum) will be sucking vapors from the charcoal canister and the fuel tank at all times instead of just at WOT. This is when you will smell gas, and this is when your canister purge valve needs to be replaced. There is no "suck pump" in the gas tank or otherwise, the vapors from the tank are collected in the charcoal canister and purged into the intake manifold using manifold vacuum, for emissions reasons.
in 98 I believe it was they switched to a non return style fuel rail and the computer actually controls fuel line pressure with an adjustable regulator, but the fuel tank is still pressurized and evacuated through the use of purge solenoids and manifold vacuum.
In 96 they simply added a sensor to the gas tank so the computer would know if a leak is developed in the pressurized system (like a broken hose, or gas cap is left off) and be able to warn you, this system reduces emissions, or at least vapors from our atmosphere, if the system has a leak it is the same as having a manifold vacuum leak and it should be repaired.
Your friend at Ford should be able to tell you the same thing. I have replaced many Ford canister purge solenoids on first gen explorer's, if you have a sucking in the gas tank, you have the intake vacuum purging the tank all the time and your system has a leak or needs a new solenoid. You can test the signal from the PCM (two wires) as well to ensure the solenoid is being told to open and close. it is also possible that your gas cap is not longer venting as it should, so you can check that as well; but I personally have never had the factory cap fail on me.
Thats why I asked if he smells fuel and also to look at the vapor purge lines at the solenoid. You can also check the chacoal canister (I dont have one) and the line from the tank. If you are low on gas then it will create this as well because there is more volume for vapors and vacuum in the tank then liquid, so it takes more pressure in the tank to purge all the vapors
