Turbo

Evaporative Control System:

SYSTEM DESCRIPTION

The Evaporative Control System consists of the fuel tank and filler cap, tank pressure control valve, a charcoal canister, a vacuum reservoir tank, two vacuum switching valves, and plumbing. The system collects fuel vapors, 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, throttle valve port 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 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 (Fuel Injected 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.

Vacuum Reservior Tank (ECS System):

VACUUM RESERVOIR TANK

The vacuum reservoir tank maintains a source of control vacuum to the tank pressure control valve during periods of operation when manifold vacuum is insufficient to hold the valve open. The reservoir tank has a built-in check valve to prevent loss of vacuum during such times.

Vacuum Switching Valve (ECS System):

VACUUM SWITCHING VALVE (TANK PRESSURE CONTROL)

A vacuum switching valve is used in line to the tank pressure control valve. This is a normally closed vacuum valve that opens when the ECM energizes its solenoid. As long as the engine is running, the valve remains open (energized) except when the ECM senses high manifold pressure (turbocharger boost), and closes the vacuum valve. This prevents loss of the vacuum signal to the tank pressure control valve during turbo boost operating conditions.

Vacuum Switching Valve (ECS System):

VACUUM SWITCHING VALVE (CANISTER PURGE)

A vacuum switching valve is used in the vacuum line to the purge control valve. This is a normally closed vacuum valve that opens when the ECM energizes its solenoid. During idle or cold operation the valve is closed (de-energized) preventing purging of the charcoal canister. The ECM will energize the valve, permitting purge, only under certain conditions. Those conditions are:

1. Engine must be at operating temperature.
2. Engine must run for a minimum length of time.
3. Vehicle must be operating above a specified road speed.
4. Throttle must be open greater than a specified angle.