W100 1/2 Ton Pickup 4WD V8-360 5.9L VIN 1 4-bbl (1988)
Fillpipe Restrictor: Description and Operation
Fuel Tank
The fuel tank mounted to the inside of the left frame rail is designed to pass a 360 degree rollover without fuel leakage. The tank contains a rollover
valve mounted on top and connected with a vapor return line to the fuel canister. Fuel feed to the fuel pump and carburetor comes from a fuel tube
assembly mounted on the top rear of the fuel tank. Lines and hoses from the fuel tank connect to the fuel pump, fuel filter, and vapor canister. On
catalyst equipped models the fuel filler tube is of a special construction, and is smaller in diameter than standard fuel nozzles to permit only unleaded
fuel to be added to the tank. The loss of fuel or vapor out of the filler neck is prevented by the use of a pressure vacuum filler cap. The relief valve
within the cap will release only under significant pressure, 13-17 kPa (1.9-2.5 psi) or vacuum, .51-1.02 kPa (.15-.30 in-hg). It is important that any
replacement cap maintain the pressure/vacuum values listed for the system to remain operative.