EGR Gas Flow Test

SYMPTOMS

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.

NOTE: Vehicle must pass CONTROL SYSTEM TEST and GAS FLOW TEST to pass EGR functional test.

1. Connect tachometer.
2. Disconnect and plug vacuum hose to EGR valve and connect vacuum pump to EGR valve nipple.
3. Start engine and disconnect Idle Air Control (IAC) motor electrical connector.
4. Slowly apply vacuum to EGR valve.
5. Engine rpm should drop as vacuum reaches 2.0 to 3.5 inches Hg, and continue to drop as more vacuum is applied, engine may even stall.
- Drop in rpm indicates exhaust gas is flowing through valve, vehicle passed GAS FLOW TEST and no further testing is necessary.
- 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.
6. Remove EGR valve, and inspect intake manifold passage.
- Clean passages if necessary.
- If no obstructions are found in intake manifold passages, replace EGR valve and retest.

NOTE: If EGR system is functioning correctly, and CHECK ENGINE lamp indicates malfunction of EGR system, check on-board diagnostic system.