Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Evaporative Emission Control System

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OPERATION



See Figure 1

The evaporative emission control system prevents the escape of fuel vapors to the atmosphere under hot soak and engine off conditions by storing the vapors in a carbon canister. Then, with the engine warm and running, the system controls the purging of stored vapors from the canister to the engine, where they are efficiently burned. Evaporative emission control components consist of the fuel vapor valve, check valve, purge control solenoid valve(s), charcoal canister and input devices.



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Fig. Fig. 1: Typical evaporative emission system schematic

Charcoal Canister

See Figure 2

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



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Fig. Fig. 2: Example of the typical EVAP charcoal canister

Purge Control Solenoid Valves

See Figure 3

The purge control solenoid valves control the flow of fuel vapor from the carbon canister to the engine. The solenoid valves are electronically controlled. Purging occurs when the engine is at operating temperature and off idle.



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Fig. Fig. 3: Example of a common purge control valve or solenoid

Check Valve

See Figure 4

The check valve releases excessive pressure or vacuum in the fuel tank to atmosphere. The valve is connected in-line with the evaporative hose and rollover/vent valve. On all engines, the valve is a 2-way check valve.



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Fig. Fig. 4: Typical check valve used to release excess pressure from the fuel tank

Fuel Vapor Valve

The fuel vapor valve prevents fuel vapors from flowing from the fuel tank at all times through the fuel tank hose. The valve is located in the fuel tank.

TESTING



See Figure 5

  1. Visually inspect the vapor and vacuum lines and connections for looseness, pinching, leakage, or other damage. If fuel line, vacuum line, or orifice blockage is suspected as the obvious cause of a malfunction, correct the cause before proceeding further.
  2.  
  3. Check the wiring and connectors to the solenoid, vane air flow meter, speed sensor and ECM for looseness, corrosion, damage or other problems. This must be done with the engine fully warmed so as to activate the purging controls.
  4.  
  5. If all checks are okay, proceed with the testing.
  6.  
  7. Check the canister purge solenoid as follows:
    1. Detach the vacuum hoses and the electrical connector from the solenoid valve.
    2.  
    3. Attach a clean test hose to port A.
    4.  
    5. Blow air through the solenoid from port A and confirm that no air exits from port B.
    6.  
    7. Apply 12 volts to one terminal of the solenoid connector and ground the other terminal.
    8.  
    9. Blow air through the solenoid from port A and confirm that air exits from port B.
    10.  
    11. If the solenoid does not function as specified, it must be replaced.
    12.  

  8.  
  9. Check the carbon canister for liquid fuel as follows:
    1. Run the engine long enough to warm it up and purge any fuel from the carbon canister.
    2.  
    3. Stop the engine and remove the canister.
    4.  

  10.  



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Fig. Fig. 5: By applying voltage to the solenoid valve, air flow between the ports should change

    1. Inspect the canister for the presence of liquid fuel, indicated by odor or by excessive weight.
    2.  
    3. Blow into the air vent in the bottom of the canister and verify that air exits readily from the fuel vapor inlet.
    4.  
    5. If the carbon canister is free of liquid fuel and air passes through it easily, proceed to the next Step. If there is fuel in the canister or air does not pass through it, replace the canister.
    6.  

  1. Check for purge line blockage as follows:
    1. Remove the purge lines (including any orifice) leading from the carbon canister to the engine intake.
    2.  
    3. Check each line for blockage by blowing through it. If air flows slowly, the line may contain an orifice that may be partially plugged.
    4.  
    5. If the line allows air to flow freely, proceed to Step 4. If air flows very slow through the line, proceed to Step 3. If air does not flow, remove the orifice, clean it thoroughly and install it in a new line, or replace the line and orifice as an assembly; proceed to Step 4.
    6.  

  2.  
  3. Check for purge line orifice blockage as follows:
    1. Remove any orifice suspected of being restricted and clean it thoroughly.
    2.  
    3. Reinstall it in the purge line and recheck it for resistance to air flow by blowing through the line.
    4.  
    5. If the line and orifice flow air more freely than when checked in Step 2, remove the orifice, replace the purge line, and reinstall the orifice, or replace the line and orifice as an assembly. The original line may contain accumulated particles.
    6.  
    7. If the line and orifice do not flow air more freely, proceed to Step 4.
    8.  

  4.  
  5. Check the fuel vapor valve as follows:
    1. Visually inspect the fuel vapor valve and its connections with the fuel tank for pinched hoses, blockage, looseness, or other mechanical damage.
    2.  
    3. If the fuel vapor valve and its connections are not damaged, remove the valve from the fuel tank.
    4.  
    5. Holding the valve in an upright position, with the tank end pointing down, blow air into the valve exhaust hose connection. Air should flow freely.
    6.  
    7. Holding the valve in the reverse position, with the tank end pointing upward, blow air into the vapor exhaust hose connection, air should not flow.
    8.  
    9. If the valve does not operate properly, replace it.
    10.  

  6.  
  7. Check the 2-way check valve function as follows:
    1. Visually inspect the check valve and its connections for hose pinching, blockage, looseness, or for evidence of other damage or leakage.
    2.  
    3. Remove the 2-way check valve.
    4.  
    5. Blow air through the valve from A to B and then from B to A. Verify that air passes easily in either direction.
    6.  
    7. If there is no evidence of leakage, and air passes easily in either direction, the check valve is okay; system testing is completed. If the valve leaks or air will not pass easily, replace the 2-way check valve.
    8.  

  8.  

REMOVAL & INSTALLATION



See Figure 6



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Fig. Fig. 6: Typical evaporative emission system component locations

Charcoal Canister
  1. Disconnect the negative battery cable.
  2.  
  3. Tag and disconnect the vapor hoses from the canister.
  4.  
  5. Remove the canister fasteners and remove the canister.
  6.  
  7. Installation is the reverse of the removal procedure.
  8.  

Fuel Vapor Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Relieve the fuel system pressure and drain the fuel tank.
  4.  
  5. Remove the fuel tank from the vehicle.
  6.  
  7. Remove the fuel vapor valve from the top of the fuel tank.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

Purge Control Solenoid Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Tag and disconnect the hoses from the valve.
  4.  
  5. If equipped, detach the electrical connector from the valve.
  6.  
  7. Remove the valve from its mounting and remove it from the vehicle.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

Check Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle.
  4.  
  5. Tag and disconnect the vapor hoses from the check valve.
  6.  
  7. Remove the check valve mounting screw and the check valve from the underside of the vehicle.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

 
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