Mazda Trucks 1987-1993 Repair Guide

Exhaust Gas Recirculation System

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OPERATION



The function of the EGR system is to reduce Oxides of Nitrogen (NOx) in the exhaust gas, which are the result of high combustion chamber temperatures. The combustion chamber temperature is reduced by directing a portion of the spent exhaust gases into the combustion chamber along with the incoming air/fuel mixture. The lower temperature in the combustion chamber results in reduced amounts of NOx.

The EGR system consists of the EGR valve and various sensors and solenoids which regulate the induction of exhaust gas.

SERVICE



  1. Check all vacuum hose to make sure they are tight and not leaking.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Disconnect the vacuum hose from the 1st EGR control valve and check that the engine continues to run smoothly. If not, replace the valve.
  6.  
  7. Connect a vacuum gauge to the hose and increase the engine speed to 2,500 rpm. The gauge should read at least 5.9 in.Hg. If not, check the water thermovalve, water temperature switch, No.1 EGR solenoid valve and, on trucks with manual transmission, the No.2 EGR vacuum switch.
  8.  
  9. Disconnect the vacuum hose from the 2nd EGR control valve and see that the engine continues to run smoothly. If not, replace the valve.
  10.  
  11. Connect a vacuum gauge to the hose and increase the engine speed to 2,500 rpm. The gauge should read at least 5.9 in.Hg. If not, check the No.2 EGR solenoid valve and the No.1 EGR vacuum switch.
  12.  
  13. Disconnect the hose from the EGR modulator valve and plug it.
  14.  
  15. Connect a length of hose to the port of the EGR modulator valve.
  16.  
  17. Increase the engine speed to 2,500 rpm and blow into the hose. See if the vacuum reading increases. If not, replace the valve.
  18.  
  19. Reconnect all hoses.
  20.  

1st EGR Control Valve

PICKUPS
  1. Start the engine and run it at idle speed. Apply vacuum to the valve. Check that the engine runs rough or stalls when 1.58 in.Hg of vacuum is applied to the valve.
  2.  
  3. If the engine does not behave as described with the specified amount of vacuum applied, replace the control valve.
  4.  

2nd EGR Control Valve

PICKUPS
  1. Start the engine and run it at idle speed. Apply vacuum to the valve. Check that the engine runs rough or stalls when 2.76 in.Hg of vacuum is applied to the valve.
  2.  
  3. If the engine does not behave as described with the specified amount of vacuum applied, replace the control valve.
  4.  

EGR Position Sensor

PICKUPS
  1. The sensor is located on top of the EGR valve. Remove the rubber boot from the connector at the EGR valve.
  2.  
  3. Disconnect the vacuum hose from the EGR valve and connect a hand vacuum pump.
  4.  
  5. Turn the ignition switch ON. Using a voltmeter, check the voltage at each terminal in the harness side of the connector.
  6.  
  7. With no vacuum applied:

    Terminal A (B/L)-0.7 volts
     
    Terminal B (B/LG)-less than 1.5 volts
     
    Terminal C (G/Y)-4.5-5.5 volts
     

  8.  
  9. With vacuum applied:

    Terminal A (B/L)-4.7 volts
     
    Terminal B (B/LG)-less than 1.5 volts
     
    Terminal C (G/Y)-4.5-5.5 volts
     

  10.  
  11. If the voltage is incorrect for terminals B and C , check the wiring harness and ECU terminals 1D , 1F and 1G .
  12.  
  13. If incorrect at terminal A . check the resistance of the sensor, then the wiring harness and then the ECU.
  14.  
  15. Check the resistance between the terminals while applying 0-5.9 in. Hg of vacuum to the EGR valve:

    Terminals B and C -5 k
     
    Terminals A and C -0.0-5.5 k
     
    Terminals A and B -0.7-6.0 k
     

  16.  

Checking Duty Solenoid Valve

PICKUPS
  1. Disconnect the vacuum hoses from the solenoid valve. Label the hoses for reinstallation.
  2.  
  3. Blow air through the vent hose and air should flow.
  4.  
  5. Disconnect the solenoid valve connector.
  6.  
  7. Connect 12 volts to one terminal of the solenoid valve and ground the other.
  8.  
  9. Blow air through the solenoid valve and verify that air does not flow.
  10.  
  11. Replace the duty solenoid valve if it does not perform as specified.
  12.  
  13. Blow air through the vacuum hose and verify that the air does not flow.
  14.  
  15. Connect 12 volts to one terminal of the solenoid and ground the other.
  16.  
  17. Blow air through the vacuum hose and verify that the air flows through. If not as specified, replace the valve.
  18.  

EGR Modulator Valve Testing

  1. Note the routing of all hoses leading to the modulator valve, especially the hose which is connected to the exhaust side of the EGR valve. Remove the EGR Modulator valve. Plug the No. 1 port and then attach a source of vacuum to the No. 3 port.
  2.  
  3. Attach a clean hose to the exhaust gas port. Blow into the end of the hose and maintain pressure. Apply vacuum to the No. 3 port and then seal off the source of vacuum. Vacuum should be maintained as long as air pressure is applied.
  4.  
  5. Stop applying air pressure. The vacuum should be released. If the valve fails to respond properly in either Step 2 or 3, replace it.
  6.  

REMOVAL & INSTALLATION



EGR Control Valve
PICKUPS
  1. Tag and disconnect the hoses at the valve.
  2.  
  3. Unbolt and remove the valve.
  4.  
  5. Installation is the reverse of removal.
  6.  

 
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