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


EGR SOLENOID TEST

1. Disconnect electrical connector from solenoid valve.
2. Remove vacuum hoses. With a solenoid wire disconnected air should flow from the vacuum port through the vent port. Energize the solenoid, air should flow through both vacuum ports. If either test fails, the solenoid valve must be replaced.
3. Connect either solenoid terminal to a ground and the other one to the battery positive terminal, then listen for clicking noise from solenoid as it is connected to battery positive terminal. If the solenoid does not click, it is defective and needs to be replaced.