Exhaust Gas Recirculation: Testing and Inspection

EGR Valve:

EGR VALVE TEST

^ With engine idling at normal operating temperature, accelerate engine to 1500 RPM and release throttle. A definite movement should be noticed in the EGR diaphragm.
^ If diaphragm does not move, check for leaking vacuum lines, faulty vacuum signal to EGR valve or defective EGR valve.
^ With engine idling at normal operating temperature, manually depress EGR valve diaphragm. Engine speed should drop immediately, indicating proper operation of the EGR valve during engine idling.
^ If there is no change in engine speed and the engine is idling properly, exhaust gases are not reaching the combustion chamber, and the probable cause is a plugged passage between the EGR valve and the intake manifold.
^ If the engine idles poorly and the speed is not greatly affected when the EGR valve diaphragm is closed, the EGR valve is not stopping the flow of exhaust gases to the combustion chambers. Check for defective hoses, incorrectly routed hoses or defective EGR valve.

Dual Function CTO:

CTO FUNCTIONAL TEST
Engine coolant temperature should be below 100° F.
^ Check vacuum lines for leaks and correct routing.
^ Disconnect vacuum line at TVS and connect it to a vacuum gauge.
^ Operate engine at approximately 1500 RPM. No vacuum should be indicated on gauge. If vacuum is indicated, replace EGR CTO valve.
^ Operate the engine until the coolant temperature exceeds 115° F.
^ Accelerate the engine to 1500 rpm. The carburetor ported vacuum should be indicated on the vacuum gauge. If not, replace the EGR CTO valve.

EGR Thermal Vacuum Switch (TVS):

TVS FUNCTIONAL TEST
Cool the air cleaner intake air below the TVS calibrated temperature, 40° F.
^ Disconnect vacuum hoses from TVS and connect an external vacuum source to the inner port.
^ Apply vacuum to TVS and observe gauge. Vacuum should be maintained by the TVS. If vacuum is not maintained, replace the TVS.
^ Start the engine and warm the air cleaner intake air to above 55° F. Vacuum should not be maintained. If vacuum is maintained, replace the TVS.