Exhaust Gas RECIRCULATION (EGR) System Operation
NOTE:
DO NOT
warm the engine until specified. Some testing must be performed when engine is cold.
- Remove cap and filter from top of EGR vacuum modulator. See Fig 1. See COMPONENT LOCATIONS under INTRODUCTION. Clean filter with compressed air. Install filter with coarse side facing upward. Install cap.
- Using a vacuum "T", connect a vacuum gauge in hose between EGR valve and EGR vacuum modulator. To ensure EGR valve is seating, start engine and check idle quality.
- If idle is smooth, go to next step. If idle is rough, disconnect vacuum hose from EGR valve. If idle is smooth, check for problems in EGR vacuum control system. If idle is still rough, EGR valve is not seating. Replace EGR valve.
- Ensure engine coolant is less than 113°F (45°C). Run engine at 2500 RPM. See CONNECTING TACHOMETER under INTRODUCTION. There should be no vacuum indicated (no EGR occurs). If any vacuum is indicated, check EGR system components.
- If no vacuum is indicated, warm engine to 122°F (50°C). Check vacuum with engine running at 2500 RPM. If no vacuum or high vacuum is indicated, check EGR system components. If low vacuum (partial EGR) is indicated, disconnect vacuum hose from port "R" of EGR vacuum modulator. See Fig 1.
- Connect a separate hose between port "R" and intake manifold. With engine running at 3500 RPM, high vacuum should be indicated (as EGR volume increases, engine should start to misfire). If no vacuum or low vacuum is indicated, check EGR system components. If high vacuum is indicated, disconnect vacuum gauge.
- Reconnect all vacuum hoses. Disconnect vacuum hose from EGR valve. Apply vacuum directly to EGR valve. If engine runs rough or stalls, system is okay. If engine does not run rough or stall, replace EGR valve.