Exhaust Gas Recirculation: Testing and Inspection

1. Check vacuum hoses and connections for looseness, pinching, leakage, splitting, blockage and proper routing.
2. Inspect the EGR valve for loose mounting bolts or a damaged flange gasket. Replace the flange gasket, and/or retorque the EGR valve to 12-18 lb-ft (16-24 Nm) if necessary before continuing to test.
3. Install a remote tachometer to the vehicle. Plug the tailpipes to increase the exhaust system back pressure, leaving a half-inch diameter opening to allow exhaust gases to escape.

Integral Back Pressure EGR Valve:

4. Remove and plug the vacuum supply hose from the EGR valve nipple.
5. START the engine, and allow it to idle with the transmission in NEUTRAL, and note the idle speed. If necessary adjust the idle speed to 600 rpm.
6. Tee into a manifold vacuum source, and apply direct manifold vacuum to the EGR valve vacuum nipple. Using a vacuum pump will not produce the desired result, since vacuum will bleed off if it is not continuously applied.
7. The idle speed should drop more than 100 rpm with continuous vacuum, and return to specification +/-25 rpm when the vacuum source is removed. If there is no drop in idle speed the EGR valve is malfunctioning and will need to be cleaned or replaced. If the idle does not return to normal when the vacuum source is removed, the EGR diaphragm is not releasing, and the valve will need to be cleaned or replaced. Refer to Powertrain Management/Emission Control Systems/Exhaust Gas Recirculation/Service and Repair for proper EGR system cleaning procedures.