Exhaust Gas Recirculation: Testing and Inspection

FUNCTIONAL TEST

A faulty EGR system can cause ignition ping, rough idle, engine stalling, sags or hesitation, and/or lack of performance. It is important that this system be free from leaks. Any hoses that are cracked or leaking should be replaced.

Inspect all vacuum hoses and connections, and replace any that are cracked, hardened, or melted. Operation of the EGR system should be checked as follows:

1. Start engine and allow to reach normal operating temperature.
2. Allow engine to run at normal idle speed and set the parking brake.
3. Allow engine to idle in neutral, then quickly accelerate engine rpm to 2000 rpm.
4. Watch the stem of the EGR valve to see if there is movement. This movement can be seen by watching the groove on the valve stem.
5. Repeat the previous step several times to verify movement of the valve. Movement of the stem indicates that the control system is functioning properly, and the EGR gas flow test can now be performed.
6. If no movement of the valve stem is visible, refer to the DIAGNOSIS test procedure in this section.


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.

EGR Diagnosis:

DIAGNOSIS

Coolant Vacuum Switch Cold Closed (CVSCC):

COOLANT VACUUM SWITCH COLD CLOSED (CVSCC)

1. Check vacuum hoses for correct routing and valve installation. The bottom port is where the source vacuum connects, and the top port connects to the air switch/relief valve.
2. Check engine coolant level.
3. With the valve installed, disconnect molded connector from valve and connect a 1/8" vacuum hose to bottom port of valve.
4. With the radiator top tank warm, about 75°F, blow through the hose.
5. If it is not possible to blow through the hose, replace the valve.
6. Start engine and allow to warm to normal operating temperature. Connect a hand operated vacuum pump to bottom port of valve and apply 10 inches Hg vacuum to the valve. If vacuum drops more than 1 inch in 15 seconds, replace the valve.