Exhaust Gas Recirculation: Testing and Inspection

Fig. 16 Connecting Vacuum Gauge:

1. Using a three-way connector tee, connect a vacuum gauge in the line between the EGR valve and the EGR vacuum modulator. Fig. 16
2. Start the engine and set at idle rpm.
3. With the coolant temperature below 117°F, check that the vacuum gauge indicates zero at 2,500 rpm.
4. Warm-up the engine until coolant temperature exceeds 127°F, and check that the vacuum gauge indicates low vacuum, (2 - 4 in.Hg) at 2,500 rpm.
5. Check that vacuum gauge indicates zero at idle speed.

Fig. 17 Testing EGR System:

6. Disconnect the vacuum hose from port R of the vacuum modulator and connect port R directly to the intake manifold with a length of vacuum hose. Fig. 17
7. Check that the vacuum gauge indicates high vacuum at 2,500 rpm. As large amounts of exhaust gas are recirculated, the engine will misfire and run rough.
8. Remove the vacuum gauge and reconnect all vacuum hoses to their proper locations.

Fig. 18 Testing EGR Valve:

9. Apply manifold vacuum directly to the EGR valve with the engine idling. Fig. 18
10. The engine should run rough and may die.
11. If no problems are found during this system test, reconnect the vacuum hose to the EGR valve. Otherwise, test each component in the EGR system.