DESCRIPTION
EGR controls NOx emissions by recirculating a controlled amount of exhaust into the combustion chamber through the intake manifold. The system consists of the EGR modulator assembly, EGR valve and Bi-Metallic Vacuum Switching Valve (BVSV).
OPERATION
Exhaust back pressure operates the EGR modulator diaphragm, which controls vacuum transmitted to the EGR valve.
Under low load, exhaust pressure is low and a spring pushes the EGR diaphragm down. The modulator valve opens to let outside air into the vacuum passage, lowering vacuum and slightly opening the EGR valve.
Under high load, the modulator diaphragm is pushed up and the modulator valve closes. Air does not enter the vacuum passage, so vacuum to the EGR valve is larger and the EGR valve opens wider.
When coolant temperature is low, the BVSV opens the EGR valve vacuum passage to outside air and the EGR valve remains closed. When coolant temperature is normal, the BVSV is closed and the EGR valve opens and closes in accordance with EGR modulator operation.
EGR SYSTEM CHECK
- With engine coolant temperature below 113°F (45°C), run engine and touch EGR diaphragm with finger to check that EGR valve diaphragm is not operating.
- Warm engine to normal operating temperature. Check that EGR valve diaphragm moves in correct direction during acceleration and deceleration. (Scheme 13)
Checking EGR Valve Diaphragm Movement. Scheme 13
BI-METALLIC SWITCHING VALVE (BVSV) CHECK
- Drain engine coolant when engine is cold. Remove BVSV from intake manifold. While keeping BVSV below 113°F (45°C), blow air into 2 BVSV nozzles individually. Air should come out of BVSV filter.
- While keeping BVSV above 140°F (60°C) in hot water, blow air into 2 BVSV nozzles individually. Air should NOT come out of BVSV filter.
- Wrap Teflon tape on BVSV threads and install BVSV to intake manifold. Reconnect vacuum hoses.
EGR MODULATOR CHECK
- Check EGR modulator filter for contamination or damage. Clean filter with compressed air.
- With engine off, disconnect modulator vacuum hoses (2). Plug one nozzle with finger and blow compressed air into other nozzle. Check that air passes through filter. (Scheme 14)
- Warm engine to normal operating temperature. Run engine at 5000 RPM. Using finger, plug one nozzle on modulator. Blow compressed air into other nozzle on modulator.
- Check that there is strong resistance to airflow. Reconnect vacuum hoses to each nozzle.
Checking EGR Modulator. Scheme 14
EGR VALVE CHECK
Remove EGR valve. Check valve for sticking and exhaust deposits. Reinstall EGR valve with a new gasket. Reconnect vacuum hoses.