EGR Gas Flow Test

1. Connect suitable tachometer to engine.
2. Disconnect vacuum hose from EGR valve and connect hand-operated vacuum pump to EGR valve nipple.
3. Start engine and allow to warm up to normal operating temperature.
4. Slowly apply vacuum to EGR valve.
5. Engine rpm should drop as vacuum reaches 3 to 5 inches Hg vacuum, and should continue to drop as more vacuum is applied, engine may even stall. This drop in rpm means that EGR gas is flowing through the system.
6. Successful completion of this test and the control system test indicates a fully-operational EGR system.
7. If engine rpm does not drop when vacuum is applied to the EGR vacuum diaphragm, then a defective EGR valve or plugged EGR passage is indicated. The EGR valve and intake manifold passage should be removed, inspected, and cleaned or replaced. Refer to MAINTENANCE PROCEDURES for cleaning and inspection procedures for the EGR valve and passages.