EGR Gas Flow Test

NOTE:
EGR system must pass CONTROL SYSTEM TEST and GAS FLOW TEST to pass FUNCTIONAL TEST.

GAS FLOW TEST

1. Connect suitable tachometer to engine.
2. Disconnect vacuum hose from EGR valve and connect hand-operated vacuum pump to EGR vacuum port.
3. Start engine and allow to warm up to normal operating temperature.
4. Slowly apply vacuum to EGR vacuum port.
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, or tube is indicated. The EGR valve, intake manifold passage, and tube assembly should be inspected and cleaned or replaced as needed. Refer to MAINTENANCE PROCEDURES for cleaning and inspection procedures for the EGR valve and passages.