Exhaust Gas Recirculation: Testing and Inspection

EGR VALVE
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, defective EGR valve or back pressure sensor.
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.

EGR CTO SWITCH
Engine coolant temperature should be below 100° F.
1. Check vacuum lines for leaks and correct routing.
2. Disconnect vacuum line at EGR valve and connect a vacuum gauge.
3. Operate engine at approximately 1500 RPM, no vacuum should be indicated on gauge. If vacuum is indicated, replace EGR CTO switch.
4. Idle engine until coolant temperature exceeds 115° F (black color coded), 160° F (yellow color coded) or 100° F on 4-151 engines.
5. Operate engine at 1500 RPM, ported carburetor vacuum should be indicated on gauge. If vacuum is not indicated, replace EGR CTO switch.

BACK PRESSURE SENSOR
1. Inspect all EGR vacuum lines for leaks and correct routing. Make certain vacuum line from EGR CTO is connected to nipple with .030 inch restriction.
2. Using a tee fitting, connect a vacuum gauge in line between EGR valve and exhaust back pressure sensor.
3. With engine idling there should be no vacuum indicated on gauge. If vacuum is indicated at idle speed, check for correct vacuum line connections. Make certain manifold vacuum is not being used as a vacuum source. If carburetor is providing vacuum, check for partially open throttle plate which could be providing premature ported vacuum to back pressure sensor.
4. Accelerate engine to 2000 RPM and observe vacuum gauge for no reading when coolant temperature is below 115° F and vacuum reading when coolant temperature is above 115° F.
5. If no vacuum was indicated during test, make certain vacuum is being applied to inlet side of back pressure sensor. If vacuum connections are correct, remove back pressure sensor and inspect spacer port and tube for restrictions. Deposits caused by carbon or lead deposits can be removed using a spiral wire brush. If no vacuum is obtained, replace back pressure sensor.

Fig. 27 Vacuum dump valve:

VACUUM SIGNAL DUMP VALVE
1. Start engine and allow to reach normal operating temperature.
2. Disconnect vacuum signal dump valve vacuum hose from connection at manifold and plug the manifold connection, Fig. 27.
3. Accelerate engine to 2000 RPM. Vacuum should be present at exhaust ports at bottom of valve. If not, replace valve.
4. Connect vacuum signal dump valve vacuum hose to manifold and accelerate engine to 2000 RPM. There should be no vacuum at exhaust ports at bottom of valve. If there is vacuum replace valve.