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    Ford Mustang 1994-1998 Repair Guide

    Evaporative Emission Control System

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    OPERATION



    See Figure 1

    Fuel vapors trapped in the sealed fuel tank are vented through the orifice vapor valve assembly in the top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister for storage until they are purged to the engine for burning.

    Purging the carbon canister removes the fuel vapor stored in the canister. The fuel vapor is purged via a Canister Purge (CANP) solenoid or vacuum controlled purge valve. Purging occurs when the engine is at normal operating temperature and off idle.



    Click image to see an enlarged view

    Fig. Fig. 1: Common Evaporative emission (EVAP) system schematic

    The evaporative emission control system consists of the following components: fuel vapor (charcoal) canister, orificed vapor valve, fuel vapor Canister Purge (CANP) solenoid, pressure/vacuum relief fuel tank filler cap, as well as the fuel tank and fuel tank filler pipe, vapor tube and fuel vapor hoses.

    Fuel Vapor (Charcoal) Canister

    See Figure 2

    The fuel vapor canister is referred to as the evaporative emissions canister on 1995-97 models.



    Click image to see an enlarged view

    Fig. Fig. 2: Cutaway view of a common fuel vapor (charcoal) canister

    The fuel vapors from the fuel tank are stored in the fuel vapor canister until the vehicle is operated, at which time the vapors will purge from the canister into the engine for consumption. The fuel vapor canister contains activated carbon, which absorbs the fuel vapor. The canister is located in the engine compartment or along the frame rail.

    Orificed Vapor Valve

    See Figure 3

    This component is also known as the evaporative emission valve on 1995-97 models.



    Click image to see an enlarged view

    Fig. Fig. 3: Cross-sectional view of the orificed vapor and rollover valve assembly

    Fuel vapor in the fuel tank is vented to the carbon canister through the vapor valve assembly. The valve is mounted in a rubber grommet at a central location in the upper surface of the fuel tank. A vapor space between the fuel level and the tank upper surface is combined with a small orifice and float shut-off valve in the vapor valve assembly to prevent liquid fuel from passing to the carbon canister. The vapor space also allows for thermal expansion of the fuel.

    CANP Solenoid

    See Figure 4

    The CANP solenoid is in line with the carbon canister and controls the flow of fuel vapors out of the canister. It is normally closed. When the engine is shut OFF , vapors from the fuel tank flow into the canister. After the engine is started, the solenoid is engaged and opens, purging the vapors into the engine. With the solenoid open, vapors from the fuel tank are routed directly into the engine.



    Click image to see an enlarged view

    Fig. Fig. 4: Note which hose is connected to each side before removing the fuel vapor canister purge regulator valve

    Pressure/Vacuum Relief Fuel Tank Filler Cap

    The fuel cap contains an integral pressure and vacuum relief valve. The vacuum valve acts to allow air into the fuel tank to replace the fuel as it is used, while preventing vapors from escaping the tank through the atmosphere. The vacuum relief valve opens after a vacuum of 0.25 psi (1.2 kPa). The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief is 2 psi (14 kPa). Fill cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.

    COMPONENT TESTING



    Fuel Vapor Canister

    Generally, the only testing done to the vapor 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.

    Do not try to check the fuel saturation of the canister by weighing it or by the intensity of the fuel odor from the canister. These methods are unreliable and inhaling gasoline fumes can be toxic.

    CANP Solenoid
    1994 MODELS
    1. Remove the CANP solenoid.
    2.  
    3. Using an external voltage source, apply 9-14 DC volts to the CANP solenoid electrical terminals. Then, use a hand-held vacuum pump and apply 11 in. Hg (53 kPa) vacuum to the manifold side nipple of the CANP solenoid.
      1. If the solenoid opens and allows air to freely pass through it, the solenoid is working properly.
      2.  
      3. If the solenoid does not allow air to pass freely while energized, replace the solenoid with a new one.
      4.  

    4.  

    1995-97 MODELS
    1. Remove the CANP solenoid.
    2.  
    3. Measure the resistance between the two CANP terminals.
      1. If the resistance is 30-90 ohms, proceed to the Step 3.
      2.  
      3. If the resistance is not 30-90 ohms, replace the CANP solenoid.
      4.  

    4.  
    5. Attach a hand-held vacuum pump to the intake manifold vacuum side of the CANP solenoid, then apply 11 in. Hg (53 kPa) of vacuum to the solenoid.
      1. If the solenoid will not hold vacuum for at least 20 seconds, replace it with a new one.
      2.  
      3. If the solenoid holds vacuum, proceed to Step 4. Keep the vacuum applied to the solenoid.
      4.  

    6.  
    7. Using an external voltage source, apply 9-14 DC volts to the CANP solenoid electrical terminals.
      1. If the solenoid opens and the vacuum drops, the solenoid is working properly.
      2.  
      3. If the solenoid does not open and the vacuum remains, replace the solenoid with a new one.
      4.  

    8.  

    EVAP System

    See Figures 5 and 6

    To perform a general evaporation emission system inspection, follow the two diagnostic charts presented here.



    Click image to see an enlarged view

    Fig. Fig. 5: Evaporative emissions (EVAP) system diagnostic chart



    Click image to see an enlarged view

    Fig. Fig. 6: Evaporative emissions (EVAP) system diagnostic chart (continued)

    REMOVAL & INSTALLATION



    Fuel Vapor Canister

    See Figures 7 and 8

    The fuel vapor canister is referred to as the evaporative emissions canister on 1995-97 models.

    1. Disconnect the vapor hoses from the canister.
    2.  
    3. Remove the mounting screws, then remove the canister.
    4.  



    Click image to see an enlarged view

    Fig. Fig. 7: Exploded view of the fuel vapor canister mounting on 3.7L models-canister mounting on 4.1L models is similar



    Click image to see an enlarged view

    Fig. Fig. 8: Exploded view of the fuel vapor canister mounting on 5.0L models

    To install:
    1. Position the canister in place, then install the mounting screws.
    2.  
    3. Attach the vapor hoses to the canister.
    4.  

    Fuel Vapor Valve

    This component is also known as the evaporative emission valve on 1995-97 models.

    1. Disconnect the negative battery cable.
    2.  
    3. Relieve the fuel system pressure.
    4.  
    5. Remove the fuel tank, as described in Fuel System of this repair guide.
    6.  
    7. Remove the fuel vapor valve from the fuel tank.
    8.  

    To install:
    1. Install the fuel vapor valve into the fuel tank.
    2.  
    3. Install the fuel tank in the vehicle.
    4.  
    5. Connect the negative battery cable.
    6.  

    CANP Solenoid
    1. Disconnect the vapor hoses from the CANP solenoid.
    2.  
    3. Unplug the electrical connector from the CANP solenoid.
    4.  
    5. Remove the purge solenoid valve from the vehicle.
    6.  

    To install:
    1. Install the CANP solenoid, then attach the engine wiring harness connector to the solenoid.
    2.  
    3. Connect the vapor hoses to the solenoid.
    4.  

    Pressure/Vacuum Relief Fuel Tank Filler Cap
    1. Unscrew the fuel filler cap.
    2.  

    The cap has a pre-vent feature that allows the tank to vent for the first3/4turn before unthreading.

    1. Remove the screw retaining the fuel cap tether and remove the fuel cap.
    2.  

    To install:
    1. Position the end of the tether against its mounting boss, then install and tighten the tether screw.
    2.  
    3. Thread the filler cap into the fuel tank filler tube, making sure to turn it clockwise until the ratchet mechanism gives off 3 or more loud clicks.
    4.  

     
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