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EGR System Mazda 626 GC

Testing & Diagnostics 3 illustrations ~677 words

DESCRIPTION

The Exhaust Gas Recirculation (EGR) system is designed to lower the burning temperature of gases in the combustion chamber, thereby reducing formation of NOx. A metered amount of exhaust gas is introduced at the intake manifold to dilute the air/fuel mixture to lower combustion temperatures.

The EGR system of 626 models, consists of EGR valve, water thermo switch and sensor, vacuum sensor, duty solenoid valve, position sensor and vacuum delay valve (with A/T).

OPERATION

Exhaust gases flow out of exhaust manifold, through EGR tubes and into EGR control valve. The EGR control valve controls exhaust gas flow in response to vacuum signals received from the vacuum amplifier or solenoid valve.

The vacuum amplifier monitors carburetor ported vacuum and controls vacuum applied at EGR control valve. The water thermo valve, water thermo switch, solenoid valve and speed switch (if equipped) allow recirculation of exhaust gases under various engine operating conditions.

Note. Refer to PISTON ENGINE VACUUM DIAGRAMS article for components used by model application.

Fig. 1: EGR System (626)
Scheme 1: EGR System (626)

DUTY SOLENOID VALVE

  1. Remove air cleaner. Disconnect duty solenoid vacuum hose from EGR control valve. Blow through solenoid vent vacuum hose (hose to air cleaner) and make sure air exhausts hose disconnected from EGR valve.
  2. Unplug solenoid valve electrical connector. Apply 12V to Brown/Red wire terminal of connector and hook jumper wire from Black/White terminal to ground (Scheme 11)
  3. Blow air through vent vacuum hose; solenoid valve should now be closed. Disconnect vacuum hose from duty solenoid to intake manifold, at manifold. Blow air through intake manifold vacuum hose; air should not pass through valve.
  4. Apply 12V to Brown/White wire terminal of connector and hook jumper wire from other Black/White terminal to ground (Scheme 11) Blow air through manifold vacuum hose; air should exhaust out vent tube.

Testing Duty Solenoid Valve Duty solenoid is located on firewall behind carburetor. Scheme 11

Scheme 11: Testing Duty Solenoid Valve Duty solenoid is located on firewall behind carburetor.
Scheme 11: Testing Duty Solenoid Valve Duty solenoid is located on firewall behind carburetor.

EGR CONTROL VALVE

  1. Bring engine to operating temperature and remove air cleaner. Plug hoses of idle compensator, thermo sensor and reed valves. Disconnect vacuum hose to EGR control valve and connect hand-operated vacuum pump to valve.
  2. Start engine and let idle. Gradually apply vacuum to valve. Engine should start to idle rough or stall when vacuum exceeds 19.7 in Hg. Clean or replace valve if idle does not change.

EGR VALVE POSITION SENSOR

  1. EGR position sensor monitors EGR valve position for the control unit. It is mounted on the EGR valve. To test sensor, unplug sensor electrical connector.
  2. Using an ohmmeter, insert leads into wire terminals of sensor connector with Green/Yellow and Blue/Orange wires. If ohmmeter reads some resistance, position sensor is not defective.

A/T Vehicles

Note. Note direction of arrow on vacuum delay valve to ensure valve is installed in properly.

  1. Disconnect and remove vacuum delay valve. Connect hand-operated vacuum pump, with gauge, to inlet side of delay valve. Hold thumb over outlet side of delay valve and apply over 19.7 in. Hg vacuum to delay valve.
  2. Release thumb from delay valve and check time required for vacuum reading to decrease from 16.7 in. Hg to 3.9 in. Hg. Specified time should be 1.3-3.3 seconds.

VACUUM SENSOR

  1. Start engine and run at idle. Connect 1 voltmeter lead to Blue wire terminal of sensor connector and other lead to ground.
  2. Voltmeter should read approximately 1V. Disconnect vacuum hose from sensor. Reading should then change to 4V. (Scheme 12)

Testing Vacuum Sensor Engine should be idling at operating temperature. Scheme 12

Scheme 12: Testing Vacuum Sensor Engine should be idling at operating temperature.
Scheme 12: Testing Vacuum Sensor Engine should be idling at operating temperature.

WATER THERMO SENSOR

Remove water thermo sensor from intake manifold. Sensor will have Blue/Red and Blue/Yellow wires attached. Place sensor in water with a thermometer and gradually heat water. Check calibration of sensor according to WATER THERMO SENSOR CALIBRATION table.

Resistance (Ohms)Water Temperature: °F (°C)
1458-17824 (-20)
2210-269068 (20)
288-352176 (80)

WATER THERMO SENSOR CALIBRATION

WATER THERMO SWITCHES

  1. Remove switch from radiator.
  2. Place the switch in water with a thermometer and gradually heat water. Check temperature at which continuity exists between both terminals of switch.
  3. The switch should show continuity at 59-67°F (15-19°C) if located in radiator, 118-126° (48-52°C) if located in intake manifold. Replace switch if it does not agree with standard value.

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