DESCRIPTION
Evaporative Emission Control System (EECS), is designed to prevent raw fuel vapors from escaping to the atmosphere. System consists of venting system which allows only vaporous fuel to be drawn into the system.
During periods of engine operation, vapors are drawn through system vent lines and into intake manifold. When engine is off, fuel vapors are stored in charcoal of vapor storage canister. Vapors are then drawn into the intake manifold when the engine is running again. (Scheme 41)
AUXILIARY CANISTER
On models with dual fuel tanks, an auxiliary canister is added to primary canister to increase canister capacity. Auxiliary canister is connected in line to purge air inlet of primary canister.
Vapors overflowing from primary canister are stored in auxiliary canister. During purging, excess vapors are routed to intake manifold for burning in engine.
CANISTER CONTROL VALVE
There are 2 types of canister control valves. (Scheme 42) The first type of valve performs function as fuel bowl vent and canister purge. When engine is not running, spring tension holds valve open allowing venting of float bowl. When engine is running, manifold vacuum pulls plunger up to close valve.
The second type of valve performs function of both vapor vent valve and purge valve. When engine is running, manifold vacuum from PCV system pulls lower diaphragm upward. This turns off venting of carburetor float bowl.
When engine is running above idle speed, control vacuum pulls upper diaphragm upward. This allows purging of canister through PCV system.
2-TUBE CANISTER
Gasoline vapors from fuel tank flow into canister and are absorbed by carbon. Canister is purged when engine is running above idle speed.
A timed vacuum source is applied to canister to draw fresh air through bottom of canister. (Scheme 43) Fresh air mixes with fuel vapors and are drawn into intake manifold to be burned in engine.
Some models are equipped with a second canister purge hose. This hose is connected to a Canister Control Valve (CCV). CCV is then connected to carburetor bowl vent line.
This allows carburetor bowl to be vented to canister, through CCV, when engine is not running. These vapors are then drawn into intake manifold once engine is started.
FUEL TANK PRESSURE CONTROL VALVE
Fuel tank pressure control valve is a spring controlled valve. When engine is running, vacuum is applied to valve and valve is opened. This allows vapors from fuel tank to vent to canister.
When engine is not running, valve closes. This causes fuel tank vapors to be vented through restriction in valve. This restriction is to retain most of fuel tank vapors in fuel tank.
PURGE SOLENOID VALVE
Solenoid valve is controlled by Electronic Control Module (ECM). When energized, purge solenoid valve turns off causing vapors to be drawn from canister through restriction and allowing high purge.
For high purge to occur, following conditions must be met: fuel control system must be operating in closed loop, time of 3 minutes must pass after starting engine, and engine must be off idle.
FUEL BOWL VENT SOLENOID
Fuel bowl vent solenoid is a grounded solenoid that is energized by ignition voltage. When solenoid is energized, valve is turned off and opens when de-energized.
THERMAL BOWL VENT VALVE
Thermal bowl vent valve, located in a section of hose from canister to carburetor, permits fuel bowl vapors to be directed to carbon-canister. When engine temperature is below 90° F (32°C), valve will close and will open when engine temperature is above 120°F (49°C).
MAINTENANCE
No adjustments are required with this system. Check system and replace air inlet filter (if equipped) in bottom of charcoal canister, every 30,000 miles. Regular inspection of system components should be made and defective components replaced as necessary.
Scheme 41
Scheme 42
Scheme 43
VAPOR VENT CONTROL VALVE
- Attach a short piece of hose to carburetor bowl vapor tube of canister and attempt to blow through it to determine if air will pass vapor vent valve into canister. If not possible to blow into canister, it must be replaced.
- Using hand vacuum pump, apply 15 in. Hg to vacuum signal tube in diaphragm assembly cover. If diaphragm does not hold vacuum for at least 20 seconds, diaphragm is leaking, and canister must be replaced.
- With vacuum still applied, again attempt to blow into the carburetor bowl vapor tube of the canister. Air should pass vapor vent valve into canister, indicating that valve is sealing properly.
- If air does enter canister past vapor vent valve, valve is not functioning properly and canister must be replaced.
TANK PRESSURE CONTROL VALVE
Install a short piece of hose on valve inlet tube (fuel tank side) and blow into hose. You should feel diaphragm pop open and air should pass through valve. If valve does not open, it should be replaced.