The EGR flow rate is controlled in 3 stages in accordance with the engine speed, load and altitude. Stage 1 is high EGR and is obtained with the throttle closed and EGR valve open. Stage 2 is low EGR and is obtained with the throttle valve and EGR open. Stage 3 is zero EGR and is obtained with the throttle open the EGR valve closed.
The engine load signal is picked up by the potentiometer installed on the injection pump control lever. The engine speed signal is generated by the electromagnetic revolution sensor on the injection pump. The throttle diaphragm and EGR valve are activated by the vacuum generated at the belt driven vacuum pump. Solenoid valves are used to convert electrical signals from the control unit into a vacuum signal.
The EGR system is not energized under the conditions that the water temperature is low. This is for good driveability and prevent unsafe cold engine conditions. A temperature sensor is used to indicate engine temperature to the EGR control unit.
- Make a thorough check of The EGR control system and make sure all connections are connected properly.
- With the engine not running, inspect the EGR control valve and throttle chamber for any signs of binding or sticking by moving the diaphragm rod upwards with a hand vacuum pump.
- With the engine running, inspect the EGR control valve and throttle valve for normal operation. Place a finger on the EGR valve diaphragm to ensure that the valve is functioning.
- When the water temperature is below 104°F (40°C). The EGR valve should not be operating.
- After the engine is to normal operating temperature, the EGR valve should be closed until the throttle valve is opened.
- If the EGR valve operates and throttle valve is closed before the engine is warm, check the temperature sensor. If the sensor checks, replace the EGR control unit under the left seat.
- If the EGR valve and throttle valve do not operate when the engine is warm. Run the engine at idle and disconnect the harness to the solenoid valve. Apply 12 volts to the solenoid and check that the EGR valve operates with the throttle closed.
See Figures 1 and 2
- Remove the EGR valve from the engine.
- Apply vacuum to the valve. If the valve moves to the full position, it is normal.
- The valve should remain open for at least 30 seconds.
- Clean the carbon from the valve and reinstall.
See Figure 3
- Remove the solenoid valves from the engine.
- Check the continuity of the air passage by sucking or blowing into the valve ports. When blowing into ports A and B and A and C , there should be no air passing through the ports. When blowing into ports B and C , there should be air passing through.
- Apply battery voltage to the solenoid valves. Check the continuity of the air passage by blowing into the valve ports. When blowing into ports A and C and B and C , there should be no air passing through the ports. When blowing into ports A and B , there should be air passing through.
See Figures 4 and 5
- Disconnect the revolution sensor electrical connector.
- Connect an ohmmeter across the sensor terminals. If continuity does not exist, replace the sensor and retest.
See Figure 6
- Disconnect the potentiometer from the top of the injection pump.
- Connect an ohmmeter between the left and center terminals with the connector snap facing upward. The resistance should change with the opening angle of the control lever.
See Figure 7
- Drain the cooling system.
- Remove the sensor from the cooling system.
- Place the sensor in a pan of water and check the resistance with the water at 66-70°F (19-21°C). The resistance should be 2.1-2.9 k-ohms.
- If the sensor resistance is not within specifications, replace the sensor.