Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Fuel Filler Cap: Description and Operation
The filler cap used on the EEC system is not vented under normal conditions. However, to prevent damage to the tank from excessive internal or
external pressure resulting from the closed system, the filler cap contains a two-way relief valve which allows the cap to vent when abnormal pressure or
vacuum develops within the tank. Installation of a fill cap from a non-emission fuel tank will render the system inoperative, since the non-emission fill
cap is vented and the system must be sealed to function properly. Also if a non-vented fill cap is installed on a conventional tank, the result will be a
serious deformation or a total collapse of the fuel tank.
