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

Mass Airflow Meter/Sensor

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OPERATION



The mass airflow meter or sensor, measures the amount of air which passes through it. The ECU uses this information to determine the operating condition of the engine, to control fuel delivery. A large quantity of air indicates acceleration, while a small quantity indicates deceleration or idle. Mazda used two types of meters in their vehicles.

One style uses a mechanical door or cone system connected to a variable resistor. The door/cone is pushed open by the incoming air, which in turn changes the resistance. The wider the door/cone is open, the larger the amount of air flow. This style is generally called a Mass Air Flow (MAF) meter.

The second style functions on a hot wire principle. A wire is heated to a certain temperature. The amount of voltage necessary to keep the wire at that temperature with air flowing over it is used to calculate airflow. The more air that flows over the wire, the cooler it will become and the more voltage will be required to heat it. This style is generally called a Mass Airflow Sensor (MAS).

TESTING



See Figures 1, 2 and 3



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Fig. Fig. 1: On plate or cone type airflow meters, verify that the plate or cone moves freely



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Fig. Fig. 2: Airflow meter electrical connections for the plate type sensors



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Fig. Fig. 3: Airflow meter electrical connections for the cone type sensors

MX-3 (except 1.6L DOHC and 1.8L V6 Engine), 1990-94 63 and Protege

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the airflow meter assembly.
  4.  
  5. Inspect the meter body for cracks and for smooth operation of the measuring plate.
  6.  
  7. Using a suitable ohmmeter, check the resistance between the terminals of the airflow meter plate.
  8.  
  9. When measuring the resistance between terminals E1 and FC (fuel pump switch), the reading should be infinity with the plate fully closed and 0 ohms when fully opened.
  10.  
  11. When measuring the resistance between terminals E2 and VS, the reading should be 200-600 ohms with the measuring plate fully closed and 20-1000 ohms when fully opened.
  12.  
  13. When measuring the resistance between terminals E2 and VC, the reading should be 200-400 ohms with the metering plate in any position.
  14.  
  15. When measuring the resistance between terminals E2 and THA (intake air thermosensor), the reading should be 13.6-18.4 kohms at -4°F; 2.21-2.69 kohms at 68°F and 493-667 ohms at 140°F with the metering plate in any position.
  16.  
  17. If not as specified, the airflow meter must be replaced.
  18.  

1990-92 626 and MX-6
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the airflow meter assembly.
  4.  
  5. Inspect the meter body for cracks and for smooth operation of the measuring plate.
  6.  
  7. Using an ohmmeter, check the resistance between the terminals of the airflow meter plate.
  8.  
  9. When measuring the resistance between terminals E1 and FC (fuel pump switch), the reading should be infinity with the plate fully closed and 0 ohms when fully opened.
  10.  
  11. When measuring the resistance between terminals E2 and VS, the reading should be 200-400 ohms with the measuring plate fully closed and 20-1000 ohms when fully opened.
  12.  
  13. When measuring the resistance between terminals E2 and VC, the reading should be 100-400 ohms with the metering plate in any position.
  14.  
  15. When measuring the resistance between terminals E2and VB, the reading should be 200-400 ohms with the metering plate in any position.
  16.  
  17. When measuring the resistance between terminals E2and THA (intake air thermosensor), the reading should be 13.6-18.4 kohms at -4°F; 2.21-2.69 kohms at 68°F and 493-667 ohms at 140°F with the metering plate in any position.
  18.  
  19. If not as specified, the airflow meter must be replaced.
  20.  

1994-95 MX-3 with 1.6L DOHC Engine, 1995-98 Protege
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the airflow meter assembly.
  4.  
  5. Inspect the meter body for cracks or damage.
  6.  
  7. Using an ohmmeter, measure the resistance between terminals C and D on the sensor.
  8.  
  9. The reading should be 2.21-2.69 kohms at 68°F (20°C).
  10.  
  11. If not as specified, replace the mass air flow sensor.
  12.  

MX-3 (1.8L), 1993-98 626/MX-6/Probe (2.5L) with V6 Engines
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the airflow meter assembly.
  4.  
  5. Inspect the meter body for cracks and for smooth operation of the measuring cone.
  6.  
  7. Using an ohmmeter, check the resistance between the terminals of the airflow meter cone.
  8.  
  9. When measuring the resistance between terminals E2 and VS, the reading should be 200-1000 ohms with the measuring cone fully closed and 20-800 ohms when fully opened.
  10.  
  11. When measuring the resistance between terminals E2 and VC, the reading should be 200-400 ohms with the metering cone in any position.
  12.  
  13. When measuring the resistance between terminals E2 and THA (intake air thermosensor), the reading should be 2000-400 ohms at 68°F (20°C) and 400-700 ohms at 140°F (60°C) with the metering cone in any position.
  14.  
  15. If not as specified, the airflow meter must be replaced.
  16.  

626/MX-6/Probe with 2.0L Engine and Millenia
  1. Back probe terminal B (center wire) of the air flow sensor electrical connector using a high impedance volt meter.
  2.  
  3. Connect the other termianl of the meter to ground.
  4.  
  5. Turn the ignition switch to the ON position.
  6.  
  7. The meter should read 1.0-1.5 volts.
  8.  
  9. Start the engine and allow to idle.
  10.  
  11. The volt meter should read 1.5-2.5 volts.
  12.  
  13. If the readings are not as specified, replace the sensor.
  14.  

REMOVAL AND INSTALLATION



See Figures 4, 5, 6 and 7

  1. Disconnect the negative battery cable.
  2.  
  3. Loosen the hose band and remove the intake hose.
  4.  



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Fig. Fig. 4: To remove the mass air flow sensor, first detach its wire harness connection



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Fig. Fig. 5: Next, remove the sensor-to-air cleaner housing retaining bolts and loosen the air intake pipe clamp



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Fig. Fig. 6: Pull the sensor out of the air cleaner housing



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Fig. Fig. 7: Inspect the air flow sensor sealing ring and replace as needed

  1. Remove the airflow meter attaching bolts and detach the wire harness connector.
  2.  
  3. Remove the airflow meter from the air cleaner housing.
  4.  
  5. Installation is the reverse order of the removal procedure.
  6.  

 
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