EGR Valve: Description and Operation

Fig. 1 EGR valve crossectional view:

The EGR system is designed to reintroduce exhaust gas into the combustion cycle in order to lower combustion temperature and reduce the formation of nitrous oxides. These vehicles use a ported EGR valve, Fig. 1, which is controlled by the EEC system through an EGR solenoid vacuum valve.

Fig. 2 EGR system diagnosis (Part 1 of 5):

Fig. 2 EGR system diagnosis (Part 2 of 5):

Fig. 2 EGR system diagnosis (Part 3 of 5):

Fig. 2 EGR system diagnosis (Part 4 of 5):

Fig. 2 EGR system diagnosis (Part 5 of 5):

SYSTEM DIAGNOSIS
Refer to Fig. 2 to diagnose driveability problems related to the EGR system.

EGR VALVE TEST
1. Ensure all vacuum hoses are properly routed and attached and show no signs of damage.
2. With engine running at idle at normal operating temperature, ensure there is no vacuum to the EGR valve.
3. Install tachometer to engine, then disconnect electrical connector from idle air bypass valve.
4. Disconnect and plug vacuum supply hose from EGR valve.
5. Check engine idle speed and adjust as necessary.
6. Using a suitable hand vacuum pump, slowly apply 5-10 inches Hg vacuum to EGR valve.
7. If engine does not stall, idle speed does not drop more than 100 RPM and/or idle speed does not return to specified idle speed with 25 RPM, the valve is defective and must be replaced.
8. Reconnect idle air bypass valve electrical connector.
9. Unplug and reconnect EGR vacuum supply hose.

EGR CONTROL SOLENOID TEST

1. Disconnect electrical connector from solenoid and measure resistance across solenoid terminals.
2. Replace solenoid if resistance is not 68-78 ohms.
3. Ensure air flows through the solenoid when energized.