Exhaust Gas RECIRCULATION (EGR) System Test
NOTE:
EGR systems contain different components depending on application. See Fig 1. When testing EGR system and components, use proper illustration to determine component location.
NOTE:
When testing EGR vacuum modulator, it may be necessary to monitor engine RPM by using scan tool. For scan tool connections, see IDLE SPEED & MIXTURE in ADJUSTMENTS
article.
- Ensure EGR vacuum modulator filter is clean and in good condition. Clean filter with compressed air (if necessary).NOTE: EGR vacuum modulator filter must be installed with coarse side facing upward, away from EGR vacuum modulator.
- Using 3-way connector, install vacuum gauge in line with vacuum hose between top of EGR valve and EGR vacuum modulator. Start engine. Ensure engine runs idles smoothly to ensure proper seating of EGR valve.
- Ensure engine coolant temperature is less than 117°F (47°C). Start and operate engine at 2500 RPM. Ensure no vacuum reading is obtained with engine at 2500 RPM. The EGR pipe should not be hot.
- Warm engine so engine coolant temperature is greater than 127°F (53°C). Operate engine at 2500 RPM and note vacuum reading. Ensure low vacuum reading is now obtained.
- Disconnect vacuum hose from port "R" on EGR vacuum modulator. See Fig 2. Using additional hose, connect port "R" on EGR vacuum modulator directly to intake manifold. High vacuum reading should be now be obtained with engine at 2500 RPM.NOTE: Engine should misfire due to large amounts of exhaust gas being injected into intake manifold.
- Remove vacuum hose and reconnect original vacuum hose to EGR vacuum modulator. To check EGR valve operation, remove and plug vacuum hose at top of EGR valve.
- Using vacuum pump, apply vacuum directly to EGR valve with engine idling. Engine should run rough or stall. If EGR system does not operate as described, each individual component should be tested. Reconnect vacuum hose at EGR valve.
- Diagnostic trouble code may have been set in Engine Control Module (ECM) while testing EGR system and Malfunction Indicator Light (MIL) on instrument panel may have come on. Clear DTC from ECM. See TESTS W/CODES article.