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 or plugged passages. Any hoses that are cracked or leaking should be replaced. If a malfunction of the EGR system is indicated by the CHECK ENGINE lamp, refer to the following service procedures, and use EGR DIAGNOSIS below. If the EGR system is functioning correctly, and the CHECK ENGINE lamp still indicates a malfunction, check the on-board diagnostic system. Refer to COMPUTERIZED ENGINE CONTROLS for on-board diagnostic checks.

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 for 70 seconds, then quickly accelerate engine rpm to 2000 to 3000 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 and plug vacuum hose from EGR valve and connect hand-operated vacuum pump to EGR valve nipple.
3. Start engine and allow to warm up to normal operating temperature.
4. Slowly apply vacuum to EGR valve.
5. Engine rpm should drop as vacuum reaches 2 to 3.5 in. 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 functional 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 removed, inspected, and cleaned or replaced. Refer to MAINTENANCE PROCEDURES for cleaning and inspection procedures for the EGR valve and passages.

EGR Diagnosis:

DIAGNOSIS

Electronically Controlled EGR Solenoid/Backpressure Transducer Assembly:

Solenoid Pack:

EGR SOLENOID TEST

1. Mark vacuum hoses on EGR Solenoid for reference, then disconnect and plug.
2. Connect a vacuum pump to the solenoid nipple that previously had the vacuum line that went to the throttle body.
3. Disconnect the EGR Solenoid valve electrical connector, and apply battery voltage to one of the solenoid terminals. Attach a jumper wire from ground to the other pin of the EGR Solenoid.
4. Using the previously attached vacuum pump, apply vacuum.
5. Verify that with voltage applied to the solenoid, vacuum holds, and with no voltage applied, vacuum does not hold. The solenoid should also make a "clicking" noise when voltage is applied and when voltage is taken away.
6. Remove battery voltage and jumper, and check the resistance of the EGR Solenoid. See SPECIFICATIONS.
7. If solenoid fails any of the previous steps, it is defective and needs to be replaced.