Non-Turbo

Evaporative Control System (4XC1 Engine):

SYSTEM DESCRIPTION

The Evaporative Control System consists of the fuel tank and filler cap, tank pressure control valve, a charcoal canister, a thermal vacuum valve, a vent switching valve (carburetor float bowl vent), a ventilation valve, and plumbing. The system collects fuel vapors from the tank and carburetor float bowl, that would otherwise be discharged into the atmosphere, and condenses them in a charcoal canister where they are temporarily stored. When the engine is started, the stored fuel and vapors are atomized with fresh air and directed to the intake to be burned in the engine. This system of vapor recovery helps not only to prevent raw hydrocarbon emissions, but also promotes fuel economy by eliminating fuel loss through evaporation.

Charcoal Canister:

CHARCOAL CANISTER

The charcoal canister is filled with activated charcoal, to condense and store fuel vapors as they enter the canister. The charcoal separates fuel vapors from air, allowing air to escape through the vent while containing the hydrocarbons. It has a valve built onto it to control purging of the fuel vapors. When the engine is not running, the diaphragm spring holds the valve closed, preventing fuel vapor from escaping through the intake system and air cleaner. When the engine is running at normal operating temperature, carburetor ported vacuum is applied to the diaphragm of the purge control valve. When sufficient vacuum is present (indicating the engine is operating under load at a minimum rpm) the purge control valve opens and fuel vapors released from the charcoal (mixed with fresh air) are drawn into the intake manifold and burned along with the normal air/fuel charge.

Fuel Filler Cap:

FUEL FILLER CAP

The fuel filler cap is designed with a two stage valve to prevent vapor loss. If vapor pressure within the tank is less than atmospheric the vacuum valve will open, allowing ambient air into the tank to equalize pressures. If vapor pressure in the tank exceeds a specific level, the pressure valve will open, allowing the excess fuel vapors to escape into the atmosphere. The pressure valve is a safety feature and does NOT open under normal conditions.

Fuel Tank (W/4XC1 Engine):

FUEL TANK

The fuel tank incorporates a vent tube that opens inside the tank, near the top so as to help prevent liquid fuel from entering the vapor recovery system and saturating the charcoal canister with fuel.

Tank Pressure Control Valve:

FUEL TANK PRESSURE CONTROL VALVE

When the engine is not running, the valve is held closed by the diaphragm spring, and fuel vapor pressure is equalized through the bypass orifice. If the tank vapor pressure is greater than atmospheric, fuel vapors flow through the bypass orifice and are collected in the charcoal canister. If the tank vapor pressure is less than atmospheric, vapors and ambient air from the charcoal canister pass through the bypass orifice in the opposite direction to equalize pressures. When the engine is running and the vacuum switching valve is open, manifold vacuum opens the tank pressure control valve and fuel vapors are allowed directly into the charcoal canister where they are condensed and stored for use.

Thermal Vacuum Valve:

THERMAL VACUUM VALVE

A thermal vacuum valve is used in line to the purge control valve. It prevents vacuum from being applied until the engine reaches the minimum operating temperature for canister purging. The thermal vacuum valve reaches into the coolant stream to measure the coolant temperature. When cold (below 165 degrees F), the valve is closed. The valve opens only at higher temperatures, insuring proper operating conditions for effective purging of the charcoal canister and adequate combustion of the purged fuel vapors.

Vent Switching Valve:

VENT SWITCHING VALVE

This is an electrically operated solenoid valve, built into the carburetor. When the engine is not running, the valve closes the float bowl vent to the air cleaner and opens the passage to the charcoal canister. When the engine is running, the valve closes the passage to the charcoal canister to block the flow of ambient air into the carburetor, and opens the float bowl vent to the air cleaner to allow fuel vapors to be drawn into the intake system for combustion.

Ventilation Valve:

VENTILATION VALVE

The ventilation valve is a vacuum operated valve that is used to improve hot fuel handling under wide open throttle conditions. When the engine is hot and the throttle is wide open, especially at high engine speeds, pressure in the float bowl is reduced due to the high velocity of air passing over the bowl vent. This may reduce the amount of fuel delivered through the main metering circuit. The ventilation valve opens the float bowl to ambient air, maintaining constant pressure in the float bowl for accurate fuel metering.