Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Evaporative Emission Control System

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OPERATION



Gasoline Engines

See Figure 1

The evaporative emission control system is designed to control the emission of gasoline vapors into the atmosphere.



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Fig. Fig. 1: Evaporative emission control system-1986-87 carbureted 323

On GLC and carbureted 323 models, the system consists of a charcoal canister, a check and cut valve, a liquid separator (wagon only), and purge control valves. On 626 models prior to 1988, the system consists of a charcoal canister, a check and cut valve (or three-way check valve), purge control valves, and on some early models, an evaporator shutter valve in the air cleaner.

On fuel injected 323s, as well as the 1988-89 626, MX-6 and 929, the system takes fuel vapor that is generated in the fuel tank and stores it in the charcoal canister when the engine is not running. This fuel vapor remains in the canister until the engine is started, at which time the fuel vapor is drawn into the intake manifold and burned. The system on these models is made up of the charcoal canister, purge control solenoid valves, a three-way check valve, a vacuum switch control valve and an electronic control unit.

Rotary Engines

See Figures 2 and 3

When raw fuel evaporates, the vapors contain hydrocarbons. To prevent these vapors from escaping into the atmosphere, the fuel evaporative emission control system was developed. The 1979-80 RX-7 models use a ventilation and check valve and a charcoal canister located in the air cleaner. The 1981-85 RX-7 with carbureted engine is equipped with a conventional charcoal canister located beside the carburetor. On these models, the flow of vapor is controlled by a purge control valve located on top of the charcoal canister. On the 1984-89 RX-7 with fuel injection, evaporative fumes from the gas tank along with those from the canister are regulated by the purge control valve, which introduces them to the intake manifold. The purge control valve is located on the side of the oil filler pipe.



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Fig. Fig. 2: Evaporative emission control system-1979-80 RX-7



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Fig. Fig. 3: Ventilation and check valve-1979-80 RX-7

On 1979-80 RX-7 models, a ventilation and check valve prevents fuel vapors from reaching the atmosphere in the following manner: When the engine is off, the fuel vapor from the gasoline in the fuel tank is trapped in the fuel tank and evaporative line until it reaches a certain pressure. When that pressure is reached, the ventilation and check valve opens, allowing fuel vapors to pass into the rotor housings and oil pan, and mix with the blow-by gases trapped there. The trapped gases are then fed into the charcoal canister, along with vapors from the fuel in the carburetor float bowl. The fuel vapors remain in the canister until the engine is started, when manifold vacuum opens the check valve, allowing all of the vapors and blow-by gases in the rotor housings/oil pan and charcoal canister to flow into the intake manifold. There, the vapors and blow-by gases mix with the air/fuel mixture to be burned in the combustion chambers.

On 1981-89 RX-7 models, a check and cut valve prevents fuel vapors from reaching the atmosphere by performing the following functions: (1) When vapor pressure in the fuel tank becomes too great, the valve releases the pressure into the charcoal canister and rotor housings to prevent the tank from bursting; (2) When vacuum pressure in the tank becomes too high, the valve allows air into the tank to prevent it from collapsing and to insure that sufficient fuel is pumped to the carburetor or throttle body and not drawn back by the vacuum in the fuel tank; (3) When the vehicle is overturned, the valve prevents fuel from flowing out of the tank. On later models, when the engine is not running, vapors from the fuel tank are fed into the charcoal canister where they are trapped by the purge valve. When the engine is running with the throttle open, manifold vacuum opens the purge valve and the vapors trapped in the canister are allowed to flow out into the throttle and dynamic chamber. There, these vapors combine with the air/fuel mixture and pass through the intake manifold to be burned in the combustion chambers. The bottom of the canister contains an air filter on most models.

SYSTEM TESTING



There are several things to check if a malfunction of the evaporative emission control system is suspected.

Piston Engines
EXCEPT 323 AND 1986-89 626/MX-6
  1. Leaks may be traced by using an infrared hydrocarbon tester. Run the test probe along the lines and connections. The meter will indicate the presence of a leak by a high hydrocarbon (HC) reading. This method is much more accurate than a visual inspection, which would indicate only the presence of a leak large enough to pass liquid.
  2.  
  3. Leaks may be caused by any of the following, so always check these areas when looking for them:
    1. Defective or worn lines
    2.  
    3. Disconnected or pinched lines
    4.  
    5. Improperly routed lines
    6.  
    7. A defective check valve
    8.  

  4.  

If it becomes necessary to replace any of the lines used in the evaporative emission control system, use only those hoses which are fuel resistant or are marked EVAP.

  1. If the fuel tank has collapsed, it may be the fault of clogged or pinched vent lines, a defective vapor separator, or a plugged or incorrect check valve.
  2.  

CARBURETED 323

See Figure 4

This test requires the use of a precisely calibrated pressure gauge and a source of compressed air. If you do not have these items on hand, it may be advisable to go to a professional for testing.

  1. Start out by testing the No. 1 and No. 2 purge control valves, as described in Steps 6 and 7 of the procedure for the 626/MX-6, which follows.
  2.  



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Fig. Fig. 4: Check and cut valve removal-carbureted 323

  1. Remove the air cleaner. Place a finger on top of the air vent solenoid valve, located on top of the carburetor. Have someone turn the ignition switch ON and OFF as you feel for operation of the solenoid. If the solenoid does not click audibly or operate so that you can feel it, replace the valve.
  2.  
  3. Test the water temperature valve, as described in Step 3 of the 626/MX-6 procedure. Replace the valve if it fails the test.
  4.  
  5. Remove the check and cut valve, noting that the horizontal connection goes to the fuel tank and the vertical connection is vented to the air. Tee a pressure gauge into the horizontal passage (normally connected to the tank). Hold the valve horizontally for proper internal air flow. Gradually admit air into the valve while watching the pressure. Air should start to flow through the valve at 0.14-0.71 psi (0.98-4.9 kpa). Connect the gauge to the vertical (vented) connection. Again, gradually admit air into the valve while watching the pressure. It should open at 0.78-1.00 psi (5.39-6.87 kpa). Replace the valve if it fails either test.
  6.  
  7. Test the vacuum switching valve, as described in Step 8 of the 626/MX-6 procedure.
  8.  
  9. Disconnect the vacuum delay valve. Connect the vacuum pump to the end of the valve away from the arrow with a length of hose 40 in. (1 meter) long. Draw a vacuum of 24 in. Hg. Then, watch as the vacuum decreases from 19.7 in. Hg to 3.9 in. Hg, timing how long it takes. It should take 0.2-1.2 seconds. If the valve fails the test, replace it.
  10.  

FUEL INJECTED 323

See Figures 5, 6 and 7

  1. Warm up the engine and allow it to run at idle speed.
  2.  
  3. Connect a voltmeter to the Y terminal of the No. 1 purge control solenoid valve, located at the top of the canister. You should read approximately 12V on the meter.
  4.  
  5. Disconnect the vacuum hose from the No. 1 purge control valve and place a finger over the opening of the hose.
  6.  



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Fig. Fig. 5: Checking No. 1 purge solenoid "Y" terminal voltage-fuel injected 323



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Fig. Fig. 6: Checking No. 1 purge control valve-fuel injected 323

  1. Increase the engine speed to 2,000 rpm and make sure that no air is being sucked into the hose.
  2.  
  3. On vehicles equipped with a manual transaxle, detach the neutral switch connector and connect a jumper wire across the terminals. On automatic transaxle-equipped vehicles, detach the inhibitor switch connector. Check the Y terminal voltage as described in Step 2.
  4.  
  5. Place your finger over the vacuum hose, then increase the engine speed to 2,000 rpm and make sure that no air is being sucked into the hose. If there is a vacuum, check the engine control unit's 2P terminal, then check the No. 1 purge control solenoid and control valves, as described in Steps 7 and 8.
  6.  



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Fig. Fig. 7: Checking No. 1 purge solenoid valve air flow-fuel injected 323

  1. To check the No. 1 purge control valve, blow through the purge control valve from port A , as shown in the illustration, and make sure that no air passes through it. Then, connect the vacuum pump to the purge control valve, also as shown in the illustration. Apply a vacuum of 4.33 in. Hg to the purge control valve, then repeat the attempt to blow air into port A . At this time, air should pass freely through port A . If not, replace the valve.
  2.  
  3. To check the No. 1 purge solenoid valve, disconnect the vacuum lines from ports A and B on the solenoid. Detach the electrical connector from the bottom of the solenoid. Blow into port A and verify that air comes out of port C . Apply battery voltage to the solenoid with a jumper wire, then blow into port A and verify that air passes freely from port B . If the valve does not function as described, replace. Proceed with the remainder of the procedure to finish the emission control system inspection.
  4.  
  5. Fasten the neutral or inhibitor switch connector, depending on the type of transaxle.
  6.  
  7. Disconnect the vacuum hose leading directly to the canister (not passing through the purge valve). Disconnect the rubber hose at the canister, then connect a vacuum source to the open end of the hose, so that air will be drawn out of the steel pipe mounted to the car body. Operate the vacuum pump. Air should be drawn into the pump freely. If the system holds vacuum, inspect the pipe or the three-way check valve (located near the fuel tank) for clogging.
  8.  

1986-89 626 AND MX-6

See Figures 8, 9 and 10

  1. Warm up the engine, then let it idle. Disconnect the vacuum hose leading to the purge control valve on top of the canister. Connect a vacuum gauge or special tester 49-9200-750A, or equivalent, to the open end of the hose. Connect a tachometer to the ignition system.
  2.  
  3. Increase the engine rpm to 2,500 and read the vacuum gauge. Vacuum must be a minimum of 5.9 in. Hg. If the vacuum is okay, go to Step 4. Otherwise, test the water temperature valve as described in Step 3.
  4.  



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Fig. Fig. 8: Disconnect vacuum hose "B" from the No. 3 purge control valve and plug it-1986-89 626 and MX-6

  1. Drain some coolant out of the system, then unscrew the water temperature valve from the intake manifold. Connect two short lengths of vacuum hose to the valve's connection points. Immerse the lower portion of the valve in a container of water with the vacuum hoses above the liquid level. Immerse a suitable thermometer in the water, then heat the water to more than 130°F (54°C) and attempt to blow air through the valve. If air passes, the valve is okay; otherwise, replace it. Reconnect the vacuum hose.
  2.  
  3. Disconnect the vacuum hose labeled B from the No. 3 purge control valve and plug it. Then, with another length of hose, connect a vacuum gauge to the open port in the purge control valve, as shown. Run the engine to more than 1,500 rpm and check for vacuum. If there is no vacuum, inspect the three-way solenoid valve, the No. 3 purge control valve and the EGR control unit's 2P terminal. Disconnect the vacuum gauge and reconnect the vacuum hose.
  4.  
  5. Disconnect the vacuum hose leading directly into the canister (not passing through the purge valve). Disconnect the hose at the canister, then connect a vacuum source to the open end of the rubber hose, so that air will be drawn out of the steel pipe mounted to the car body. Operate the vacuum pump. Air should be drawn into the pump freely. If the system holds vacuum, inspect the pipe or the three-way check valve (located near the fuel tank) for clogging.
  6.  
  7. Attempt to blow air into the port labeled A . No air should pass into it.Connect the vacuum pump to the purge control valve, as shown in the illustration. Apply a vacuum of 4.33 in. Hg to the purge control valve. Then, repeat the attempt to blow air into A . This time, air should flow. Otherwise, replace the purge control valve.
  8.  



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Fig. Fig. 9: Blow into port "A" to begin inspection of the No. 1 purge control valve-1986-89 626 and MX-6



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Fig. Fig. 10: Testing the three-way check valve-1986-89 626 and MX-6

  1. Disconnect the hose referred to in Step 5 at the metal pipe, but this time, blow into the hose with it still connected to the canister. Air should flow freely. Otherwise, replace the No. 2 purge valve.
  2.  
  3. First, label the connecting hoses, then remove the No. 3 purge control valve. Blow into the center port on the flat side of the valve and check for air flow leaving the outboard port on the flat side. There should be no air flow without vacuum being applied to the valve. Apply vacuum of 2.95 in. Hg to the single port located on the convex side of the valve. Then, blow through the center port again, as you did at the beginning of this step. Air should now flow out of the outboard port. Install a new valve, if necessary, or reinstall the old one with all hoses properly connected, according to your labeling.
  4.  
  5. Remove the three-way check valve located on the gas tank vent line near where the filler pipe connects with the fuel tank. Blow through Port A and make sure air comes out Port B . Seal off Port B and blow again from Port A . Air should flow out of Port C . Now, block Port B and blow through port C . Air should come out of Port A . If the valve fails any of these tests, replace it.
  6.  
  7. The three-way solenoid valve is located at the right of the three valves mounted on the fender well. Label, then disconnect the two hoses at the bottom of the valve. Connect a short length of hose to the port leading into the side of the valve near the bottom, leaving the vertical port (which discharges out in a downward direction) open. First, blow through the hose and check for discharge of air through the filter at the top. Then, energize the valve by applying battery voltage to the electrical connector at the top with a jumper wire. Now, when you blow through the hose, air should be discharged through the port at the bottom of the valve. If the valve fails either test, replace it.
  8.  

Rotary Engines
CARBURETED MODELS

When the car is parked after operation for some distance, the fuel in the float chamber tends to evaporate and enter the intake manifold through an inner air vent. This, in turn, causes the fuel mixture to become too rich and flood the engine. To prevent this chain of events, an air vent solenoid valve is installed on the carburetor. When the engine is not running (ignition switch in the OFF position), a plunger attached to the air vent solenoid is pulled out, which allows the fuel vapors in the float bowl to be fed into the charcoal canister, where they are stored. When the engine is running (ignition switch turned ON ), the solenoid closes. This opens the air vent in the carburetor and closes off the passage to the charcoal canister. Testing of the air vent solenoid valve is performed as follows:

  1. Check the air vent hose for cracking or other damage.
  2.  
  3. Disconnect the air vent hose from the ventilation pipe.
  4.  
  5. Slowly blow through the hose and make sure that air passes through the air vent solenoid valve.
  6.  
  7. Turn the ignition switch to the ON position.
  8.  
  9. Slowly blow through the hose; air should not pass through the air vent solenoid. If it does, check the solenoid wiring or replace the solenoid.
  10.  

FUEL INJECTED MODELS-EXCEPT 1987

See Figure 11

  1. Disconnect and remove the check and cut valve, as described below.
  2.  

Perform the test with the valve held horizontally. Otherwise, the weight of the valve will cause it to move out of position and close the passage.

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Fig. Fig. 11: Testing the check and cut valve-fuel injected RX-7

  1. Connect a pressure gauge to the passage from the fuel tank (port A ).
  2.  
  3. Blow into the valve through port A . Check that the valve opens at 0.14-0.71 psi (0.97-4.90 kpa).
  4.  
  5. Remove the pressure gauge and connect it to the passage that vents to the atmosphere (port B ).
  6.  
  7. Blow into the valve through port B and check that the valve opens at 0.78-1.00 psi (5.38-6.89 kpa).
  8.  
  9. If the valve does not function as described, replace it.
  10.  

1987 FUEL INJECTED MODELS
  1. Disconnect and remove the check and cut valve.
  2.  
  3. Blow into the valve through port A and make sure that air comes out of port B .
  4.  
  5. Block port B and confirm that air comes out of port C .
  6.  
  7. Block port B and draw air through port A . Air should pass through from port C .
  8.  
  9. If the valve does not function as described, replace it.
  10.  

REMOVAL & INSTALLATION



Check and Cut Valve
  1. Raise and safely support the rear of the vehicle.
  2.  
  3. Unfasten the hose bands and disconnect the evaporative hoses from the check and cut valve.
  4.  
  5. Remove the check and cut valve.
  6.  
  7. Installation is the reverse of removal. Be sure to route the hoses properly.
  8.  

 
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