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    Ford Pick-Ups/Expedition/Navigator 1997-2000

    Evaporative Emission Controls

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    OPERATION



    Changes in atmospheric temperature cause fuel tanks to breathe, that is, the air within the tank expands and contracts with outside temperature changes. If an unsealed system was used, when the temperature rises, air would escape through the tank vent tube or the vent in the tank cap. The air which escapes contains gasoline vapors.

    The Evaporative Emission Control System provides a sealed fuel system with the capability to store and condense fuel vapors. When the fuel evaporates in the fuel tank, the vapor passes through the EVAP emission valve, through vent hoses or tubes to a carbon filled evaporative canister. When the engine is operating the vapors are drawn into the intake manifold and burned during combustion..

    A sealed, maintenance free evaporative canister is used. The canister is filled with granules of an activated carbon mixture. Fuel vapors entering the canister are absorbed by the charcoal granules. A vent cap is located on the top of the canister to provide fresh air to the canister when it is being purged. The vent cap opens to provide fresh air into the canister, which circulates through the charcoal, releasing trapped vapors and carrying them to the engine to be burned.

    Fuel tank pressure vents fuel vapors into the canister. They are held in the canister until they can be drawn into the intake manifold. The canister purge valve allows the canister to be purged at a pre-determined time and engine operating conditions.

    Vacuum to the canister is controlled by the canister purge valve. The valve is operated by the PCM. The PCM regulates the valve by switching the ground circuit on and off based on engine operating conditions. When energized, the valve prevents vacuum from reaching the canister. When not energized the valve allows vacuum to purge the vapors from the canister.

    During warm up and for a specified time after hot starts, the PCM energizes (grounds) the valve preventing vacuum from reaching the canister. When the engine temperature reaches the operating level of about 120°F (49°C), the PCM removes the ground from the valve allowing vacuum to flow through the canister and purges vapors through the throttle body. During certain idle conditions, the purge valve may be grounded to control fuel mixture calibrations.

    The fuel tank is sealed with a pressure-vacuum relief filler cap. The relief valve in the cap is a safety feature, preventing excessive pressure or vacuum in the fuel tank. If the cap is malfunctioning, and needs to be replaced, ensure that the replacement is the identical cap to ensure correct system operation.

    OBD-II EVAP System Monitor

    Some of the models covered in this guide have added system components due to the EVAP system monitor incorporated in the OBD-II engine control system. A pressure sensor is mounted on the fuel tank which measures pressure inside the tank, and a purge flow sensor measures the flow of the gases from the canister into the engine. The purge valve is now called the Vapor Management Valve (VMV). It performs the same functions as the purge valve, however it looks slightly different. A canister vent solenoid is mounted on the canister, taking the place of the vent cap, providing a source of fresh air to the canister.

    The PCM can store trouble codes for EVAP system performance, a list of the codes is provided later in this information. Normal testing procedure can be used, see EVAP System Component Testing in this Section.

    TESTING



    Evaporative Emissions Canister


    Click image to see an enlarged view

    Fig. Fig. 1 EVAP canister assembly

    Generally, the only testing done to the canister is a visual inspection. Look the canister over and replace it with a new one if there is any evidence of cracks or other damage.

    Evaporative Hoses and Tubes

    Inspect all system hoses and tubes for signs of damage or cracks. Any damage or leakage must be repaired.

    Evaporative Emissions Valve


    Click image to see an enlarged view

    Fig. Fig. 2 EVAP emissions valve assembly

    Inspect the valve for open air passage through the orifice. The valve is molded directly to the fuel tank and is not serviceable separately. If the orifice is blocked, replace the fuel tank.

    Canister Purge Valve/Vapor Management Valve


    Click image to see an enlarged view

    Fig. Fig. 3 Canister purge valve assembly

    1. Remove the canister purge valve.
    2.  
    3. Measure the resistance between the two valve terminals.
      1. If the resistance is between 30-36 ohms, proceed to the Step 3.
      2.  
      3. If the resistance is not between 30-36 ohms, replace the valve.
      4.  

    4.  
    5. Attach a hand-held vacuum pump to the intake manifold vacuum side of the valve, then apply 16 in. Hg (53 kPa) of vacuum to the valve.
      1. If the valve will not hold vacuum for at least 20 seconds replace it with a new one.
      2.  
      3. If the valve holds vacuum, proceed to Step 4. Keep the vacuum applied to the valve.
      4.  

    6.  
    7. Using an external voltage source, apply 9-14 DC volts to the valve electrical terminals.
      1. If the valve opens and the vacuum drops, the valve is working properly. Check power and ground circuits.
      2.  
      3. If the valve does not open and the vacuum remains, replace the valve is faulty.
      4.  

    8.  

    REMOVAL & INSTALLATION



    Evaporative Emissions Valve
    1. Raise and support the vehicle.
    2.  
    3. Remove the fuel tank. See .
    4.  
    5. Disconnect the vapor hose from the valve.
    6.  
    7. Twist and remove the valve.
    8.  
    9. Installation is the reverse of removal.
    10.  

    Pressure Sensor
    1. Raise and support the vehicle.
    2.  
    3. Remove the fuel tank. See .
    4.  
    5. Detach the connector from the sensor.
    6.  
    7. Twist and remove the sensor.
    8.  
    9. Installation is the reverse of removal.
    10.  

    Evaporative Emissions Canister
    F-150, F-250, EXPEDITION, NAVIGATOR AND 1999-00 SUPER DUTY MODELS


    Click image to see an enlarged view

    Fig. Fig. 4 The EVAP canister is located under the vehicle near the spare tire-F-150, F-250, Expedition, Navigator and 1999-00 super duty models

    1. Raise and safely support the vehicle securely on jackstands.
    2.  
    3. Detach the canister vent solenoid electrical connector.
    4.  
    5. Remove the canister retaining bolts.
    6.  
    7. Disconnect the canister vent solenoid hose assembly.
    8.  
    9. Lower the canister and bracket.
    10.  
    11. Loosen the evaporative emissions (EVAP) canister purge outlet tube clamp and disconnect the tube.
    12.  
    13. Remove the canister vent solenoid from the canister.
    14.  
    15. Remove the evaporative emissions canister.
    16.  

    To install:

    Lubricate all O-rings with Merpol® or equivalent meeting Ford specification ESE-M99B144-B before installation.

    1. Installation is the reverse of removal.
    2.  

    1997-98 F-250HD, F-350 AND F-SUPER DUTY
    1. Label and disconnect the vapor hoses from the canister.
    2.  
    3. Remove the retaining screw for the canister bracket.
    4.  
    5. Lift the canister to disengage the retaining tab on the back of the canister and remove the canister.
    6.  

    To install:

    1. Installation is the reverse of removal.
    2.  

    Canister Purge Valve/Vapor Management Valve
    F-150, F-250, EXPEDITION, NAVIGATOR AND 1999-00 SUPER DUTY MODELS
    1. Detach the electrical connector from the evaporative emission (EVAP) canister purge valve.
    2.  
    3. Label and disconnect the evaporative emissions vacuum control hose.
    4.  
    5. Label and disconnect the two fuel vapor tubes.
    6.  
    7. Remove the two retaining bolts and remove the evaporative emission canister purge valve.
    8.  

    To install:

    1. Installation is the reverse of removal.
    2.  

    1997-98 F-250HD, F-350 AND F-SUPER DUTY
    1. Detach the purge valve electrical connector.
    2.  
    3. Label and remove the EVAP hoses from the purge valve and remove the valve.
    4.  

    To install:

    1. Installation is the reverse of removal.
    2.  

     
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