EGR Control System

Fig. 6 EGR vacuum system:

1. Ensure that coolant temperature is less than 140°F, connect suitable vacuum gauge inline between VSV and EGR valve, and connect suitable tachometer following manufacturer's instructions.
2. Start engine and observe vacuum gauge reading. If gauge indicates vacuum, check for grounded wiring between coolant sensor and switching valve, or defective sensor or valve.
3. Run engine until it reaches normal operating temperature, return engine to idle and note vacuum gauge reading.
4. Gauge reading should be 12.4 - 13.03 inches Hg. If vacuum is indicated but reading is not within specifications, proceed as follows:
a. Check vacuum hoses between EGR valve and vacuum pump, Fig. 6, and repair as needed.
b. If vacuum hoses are satisfactory, test VRV and pump and repair as needed.
6. If no vacuum is present at idle with coolant temperature above 172°F, proceed as follows:
a. With engine running at idle, disconnect electrical connectors from VSV.
b. Connect test lamp between suitable ground and B+ feed to VSV. If lamp fails to light, check for open in feed circuit or defective control module.
c. Connect test lamp between VSV leads in harness. If lamp fails to light, check ground circuit wiring, coolant switch and idle switch, and repair as needed.
d. If test lamp lights in both tests, check for defective VSV and replace as needed.
7. Move injection pump lever slightly off idle position (approximately .030 inch) and observe gauge reading.
8. If reading does not drop to zero, check idle switch and repair as needed.
9. Slowly accelerate engine from idle position to 3000 RPM noting vacuum gauge reading.
10. Gauge reading should be approximately 12.4 inches Hg at idle, reading should progressively decrease to 9.4 inches Hg at 2800 RPM, then reading should drop to zero above 2800 RPM.
11. If vacuum readings are higher or lower than specified in the 1000 - 2800 RPM range, check VRV and repair as needed.
12. If no vacuum is present in 1000 - 2800 RPM range, or if vacuum reading does not fall to zero above 2800 RPM, proceed as follows:
a. Disconnect electrical connectors to VSV, connect test lamp between connector terminals and repeat step 9.
b. If lamp does not remain on with engine running at 1000 - 2800 RPM and turn off with speed above 2800 RPM, check wiring between VSV and control module and repair as needed. If wiring is satisfactory, test control module and sensors as shown in Fig. 4.