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    GM Camaro/Firebird 1993-1998 Repair Guide

    Evaporative Emission Controls

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    OPERATION



    See Figures 1, 2, 3 and 4

    The Evaporative Emission Control System (EECS) is designed to prevent fuel tank vapors from being emitted into the atmosphere. When the engine is not running, gasoline vapors from the tank are stored in a charcoal canister, mounted inside the left rear wheel well. The charcoal canister absorbs the gasoline vapors and stores them until certain engine conditions are met and the vapors can be purged and burned by the engine. In some vehicles, any liquid fuel entering the canister goes into a reservoir in the bottom of the canister to protect the integrity of the carbon element in the canister above. Three different methods are used to control the purge cycle of the charcoal canister.



    Click image to see an enlarged view

    Fig. Fig. 1: EVAP canister location-1998 vehicle shown, other years similar



    Click image to see an enlarged view

    Fig. Fig. 2: Typical evaporative emission canister

    First, the charcoal canister purge cycle is controlled by throttle position without the use of a valve on the canister. A vacuum line connects the canister to a ported vacuum source on the throttle body. When the throttle is at any position above idle, fresh air is drawn into the bottom of the canister and the fuel vapors are carried into the throttle body at that port. The air/vapor flow volume is only what can be drawn through the vacuum port and is fairly constant.



    Click image to see an enlarged view

    Fig. Fig. 3: EVAP system schematic-3.4L engine shown

    Second, the flow volume is modulated with throttle position through a vacuum valve. The ported vacuum from the throttle body is used to open a diaphragm valve on top of the canister. When the valve is open, air and vapors are drawn into the intake manifold, usually through the same manifold port as the PCV system. With this method, the purge valve cycle is slaved to the throttle opening; more throttle opening, more purge air flow.



    Click image to see an enlarged view

    Fig. Fig. 4: Evaporative emission control system schematic-5.7L (VIN P) engine shown

    And third, the charcoal canister purge valve cycle is controlled by the PCM through a solenoid valve on the canister. When the solenoid is activated, full manifold vacuum is applied to the top of the purge valve diaphragm to open the valve all the way. A high volume of fresh air is drawn into the canister and the gasoline vapors are purged quickly. The PCM activates the solenoid valve when the following conditions are met:



    The engine is at normal operating temperature.
     
    After the engine has been running a specified period of time.
     
    Vehicle speed is above a predetermined speed.
     
    Throttle opening is above a predetermined value.
     

    A vent pipe allows fuel vapors to flow to the charcoal canister. On some vehicles, the tank is isolated from the charcoal canister by a tank pressure control valve, located either in the tank or in the vapor line near the canister. It is a combination roll-over, integral pressure and vacuum relief valve. When the vapor pressure in the tank exceeds 0.72 psi (5 kPa), the valve opens to allow vapors to vent to the canister. The valve also provides vacuum relief to protect against vacuum build-up in the fuel tank and roll-over spill protection.

    Poor engine idle, stalling and poor driveability can be caused by an inoperative canister purge solenoid, a damaged canister or split, damaged or improperly connected hoses.

    The most common symptom of problems in this system is fuel odors coming from under the hood. If there is no liquid fuel leak, check for a cracked or damaged vapor canister, inoperative or always open canister control valve, disconnected, misrouted, kinked or damaged vapor pipe or canister hoses; or a damaged air cleaner or improperly seated air cleaner gasket.

    TESTING



    Pressure Control Valve

    See Figures 5 and 6

    1. Using a hand-held vacuum pump, apply a vacuum of 15 in. Hg (51 kPa) through the control vacuum signal tube to the purge valve diaphragm. If the diaphragm does not hold vacuum for at least 20 seconds, the diaphragm is leaking. Replace the control valve.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 5: Cross-sectional view of the EVAP pressure control valve-3.4L engine



    Click image to see an enlarged view

    Fig. Fig. 6: EVAP pressure control valve components-5.7L (VIN P) engine shown

    1. With the vacuum still applied to the control vacuum tube, attach a short piece of hose to the valve's tank tube side and blow into the hose. Air should pass through the valve. If it does not, replace the control valve.
    2.  

    Canister Purge Control Valve
    1. Connect a clean length of hose to the fuel tank vapor line connection on the canister and attempt to blow through the purge control valve. It should be difficult or impossible to blow through the valve. If air passes easily, the valve is stuck open and should be replaced.
    2.  
    3. Connect a hand-held vacuum pump to the top vacuum line fitting of the purge control valve. Apply a vacuum of 15 in. Hg (51kPa) to the purge valve diaphragm. If the diaphragm does not hold vacuum for at least 20 seconds the diaphragm is leaking. Replace the control valve. If it is impossible to blow through the valve, it is stuck closed and must be replaced.
    4.  
    5. On vehicles with a solenoid activated purge control valve, unplug the connector and use jumper wires to supply 12 volts to the solenoid connections on the valve. With the vacuum still applied to the control vacuum tube, the purge control valve should open and it should be easy to blow through. If not, replace the valve.
    6.  

    REMOVAL & INSTALLATION



    EVAP Canister

    See Figures 7 and 8

    1. Disconnect the negative battery cable.
    2.  
    3. Raise and properly support the vehicle.
    4.  
    5. If necessary, remove the drivers side rear wheel and tire assembly.
    6.  
    7. Remove the drivers side rear wheel housing liner.
    8.  
    9. Tag and disconnect the vacuum hoses from the canister.
    10.  
    11. Loosen the screw or release the latch securing the canister retaining bracket.
    12.  
    13. Remove the canister from the vehicle.
    14.  



    Click image to see an enlarged view

    Fig. Fig. 7: EVAP canister location and mounting-1993-97 vehicles



    Click image to see an enlarged view

    Fig. Fig. 8: The EVAP canister is secured to a mounting bracket-1998 vehicles

    To install:
    1. Install the canister into the retaining bracket.
    2.  
    3. Tighten the screw or fasten the latch securing the canister retaining bracket, as applicable.
    4.  
    5. Connect the hoses to the canister as tagged during removal.
    6.  
    7. Install the rear wheel housing liner and wheel and tire assembly, then carefully lower the vehicle.
    8.  
    9. Connect the negative battery cable.
    10.  

    Filter

    Not all models use canisters with replaceable filters.

    1. Remove the vapor canister.
    2.  
    3. Pull the filter out from the bottom of the canister.
    4.  
    5. Install a new filter and then replace the canister.
    6.  

    Canister Purge Solenoid Valve

    See Figures 9, 10, 11 and 12

    1. Disconnect the negative battery cable.
    2.  
    3. If necessary, remove the ignition system test connector.
    4.  
    5. Detach the electrical connector and hoses from the solenoid.
    6.  
    7. For 1993-97 vehicles, remove the bracket and solenoid from the intake manifold.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 9: Exploded view of the canister purge solenoid valve mounting-3.4L engine



    Click image to see an enlarged view

    Fig. Fig. 10: The EVAP canister purge solenoid valve is secured to a bracket-1995 5.7L engine shown



    Click image to see an enlarged view

    Fig. Fig. 11: Exploded view of the EVAP canister purge solenoid valve-1997 5.7L engine shown

    1. For 1998 vehicles, bend the tab on the mounting bracket, then remove the solenoid valve.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 12: EVAP canister purge solenoid valve mounting-1998 vehicle shown

    To install:
    1. For 1998 vehicles, position the solenoid valve on the mounting bracket and bend the retaining tab over.
    2.  
    3. For 1993-97 vehicles, install the solenoid valve and bracket to the intake manifold. Install the retaining bolt and tighten to 7 ft. lbs. (10 Nm) for the 3.4L engine and to 52 inch lbs. (5.8 Nm) for the 5.7L (VIN P) engine.
    4.  
    5. Attach the hoses and electrical connector to the solenoid.
    6.  
    7. If removed, install the ignition system test connector.
    8.  
    9. Connect the negative battery cable.
    10.  

    Tank Pressure Control Valve
    1. Disconnect the negative battery cable.
    2.  
    3. Tag and disconnect the vacuum hoses from the control valve.
    4.  
    5. Remove the mounting hardware.
    6.  
    7. Remove the control valve from the vehicle.
    8.  
    9. Installation is the reverse of the removal procedure.
    10.  

    Vent Valve

    See Figure 13

    1. Disconnect the negative battery cable.
    2.  
    3. Unfasten the EVAP canister vent valve from the bracket.
    4.  
    5. Detach the vent valve electrical connector.
    6.  
    7. Loosen the vent hose clamp, then remove the hose from the vent valve.
    8.  
    9. Remove the vent valve from the vehicle.
    10.  



    Click image to see an enlarged view

    Fig. Fig. 13: A EVAP vent valve is used on 1998 vehicles

    To install:
    1. Connect the vent hose to the EVAP canister vent valve, then tighten the hose clamp securely.
    2.  
    3. Attach the EVAP canister vent valve electrical connector.
    4.  
    5. Install the vent valve to the bracket.
    6.  
    7. Connect the negative battery cable.
    8.  

    EVAP Purge Vacuum Switch

    See Figures 14 and 15

    1. Disconnect the negative battery cable.
    2.  
    3. Detach the electrical connector.
    4.  
    5. Tag and disconnect the vacuum lines from the vacuum switch.
    6.  
    7. Remove the retaining bolt or bend the tab on the mounting bracket, then remove the EVAP vacuum switch from the bracket.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 14: Exploded view of the EVAP purge vacuum switch-1997 3.8L engine shown



    Click image to see an enlarged view

    Fig. Fig. 15: EVAP purge vacuum switch (1), bracket (2), retaining bolt (4) and mount (3)-1997 5.7L engine shown

    1. Installation is the reverse of the removal procedure.
    2.  

     
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