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    Honda Civic/CRX/del Sol 1984-1995 Repair Guide

    Fuel Evaporative Emission Control System

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    OPERATION



    See Figure 1

    The function of this system is to minimize the amount of fuel vapors escaping into the air. The system consists of a charcoal canister, a canister vapor purge system, tank vapor control system, and on the carbureted engine, a carburetor vapor control system. When fuel evaporates in the tank or carburetors, the vapors pass through the vent hoses to the charcoal canister where they are stored. The purge control system uses solenoid valves operated by the ECU to draw fresh air into the canister and carry the vapors into the intake manifold when the engine is running.



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    Fig. Fig. 1: Common fuel system layout including emissions control devices-1992-95 vehicles

    Charcoal Canister

    See Figures 2, 3 and 4

    A sealed, maintenance-free charcoal canister is used on all vehicles and is located in the engine compartment. Fuel tank vents lead to the canister. Fuel vapors are temporarily held in the canister's activated charcoal until they can be drawn into the intake manifold and burned in the combustion chamber.



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    Fig. Fig. 2: Evaporative emmission control system components-1984-87 vehicles



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    Fig. Fig. 3: Evaporative emmission control system components-1988-91 vehicles



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    Fig. Fig. 4: Evaporative emmission control system components-1992-95 vehicles

    SERVICE



    Vapor Purge Control System

    This system consists of a purge control diaphragm valve on top of the canister and a solenoid valve controlling the vacuum signal. In the vapor line between the tank and the charcoal canister is a 2-way valve which provides some resistance to flow in either direction. It allows air to flow into the tank as fuel is drawn out. It also allows fuel vapor to travel the other way to the canister when the pressure in the fuel tank is above the valve opening pressure.

    Complete testing of the purge control system on a vehicle with an automatic transmission requires running the engine with the transmission in gear and the drive wheels turning.

    FUEL INJECTED ENGINE

    See Figures 5, 6, 7 and 8

    1. With the engine cold, disconnect the vacuum hose from the top of the purge control diaphragm and connect a vacuum gauge to it. The gauge on a hand vacuum pump can be used.
    2.  
    3. With the engine cold and at idle, the solenoid valve should be closed. The gauge should show no vacuum when the engine is first started. As the engine warms up, the solenoid valve will open to open the purge control valve. On CRX SI, the valve should open in about 10 seconds.
    4.  



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    Fig. Fig. 5: Connecting a vacuum pump to the purge control valve



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    Fig. Fig. 6: Terminal connectors for testing the purge cut-off solenoid valve-fuel injected engines



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    Fig. Fig. 7: Testing the purge fresh air hose using a vacuum gauge-fuel injected engines



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    Fig. Fig. 8: Testing the two-way valve using a vacuum pump/gauge-fuel injected engines

    1. If there is no vacuum by the time the radiator fan has run, check the purge cut-off solenoid and the wiring to it. The solenoid should have 12 volts at the black/yellow wire when the ignition switch is ON . The ECU completes the ground circuit.
    2.  
    3. Reconnect the vacuum line to the valve and connect the gauge to the bottom of the canister where fresh air is admitted. Run the engine at about 3500 rpm. If no vacuum appears when the solenoid valve is open, the canister may be broken. Test the 2-way valve and make sure the fuel filler cap is not leaking.
    4.  
    5. Stop the engine. To test the 2-way valve, remove the fuel filler cap, disconnect the fuel tank vent line, connect a hand vacuum pump to the line and draw a vacuum. It should momentarily stabilize at 0.2-0.6 in. Hg (5-15mm Hg) of vacuum.
    6.  
    7. At the same line, apply low air pressure. The pressure should momentarily stabilize at 0.4-1.4 in. Hg (10-35mm Hg) of vacuum. Correct vacuum and pressure readings mean the 2-way valve is functioning and the tank is venting properly.
    8.  

    CARBURETED ENGINE

    See Figures 9, 10 and 11



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    Fig. Fig. 9: Testing the purge fresh air hose using a vacuum gauge-carbureted engines



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    Fig. Fig. 10: Testing the canister purge valve-carbureted engines

    1. Raise and safely support the front of the vehicle so the drive wheels are free to turn. With the engine cold, disconnect vacuum hose No. 19 from the top of the purge control diaphragm and connect a vacuum gauge to it. The gauge on a hand vacuum pump can be used.
    2.  
    3. Start the engine and run at idle. There should be no vacuum. If there is vacuum, check for 12 volts to the purge cut-off solenoid valve at the orange wire. If there is voltage, the ECU is getting an incorrect input signal or the ECU is faulty. If there is no voltage, the solenoid valve is probably stuck open.
    4.  
    5. Warm the engine until the radiator fan runs. Put the shift selector in 2 and run the engine at 3500 rpm. If the vacuum lines are routed correctly and not leaking, there should be vacuum. If there is no vacuum and there is power to the purge cut-off solenoid at the orange wire when the drive wheels are turning at about 20 mph, the solenoid ground or solenoid is probably faulty. If there is no power to the solenoid, go to the ECU self-diagnostic test.
    6.  
    7. Reconnect the vacuum line to the valve and connect the gauge to the bottom of the canister where fresh air is admitted. Run the engine at about 3500 rpm. If no vacuum appears when the solenoid valve is open, the canister may be broken. Test the 2-way valve and make sure the fuel filler cap is not leaking.
    8.  
    9. Stop the engine. To test the 2-way valve, remove the fuel filler cap, disconnect the fuel tank vent line, connect a hand vacuum pump to the line and draw a vacuum. It should momentarily stabilize at 0.2-0.6 in. Hg (5-15mm Hg) of vacuum.
    10.  
    11. At the same line, apply low air pressure. The pressure should momentarily stabilize at 0.4-1.4 in. Hg (10-35mm Hg) of vacuum. Correct vacuum and pressure readings mean the 2-way valve is functioning and the tank is venting properly.
    12.  



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    Fig. Fig. 11: Testing the two-way valve using a vacuum pump/gauge-carbureted engines

     
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