The egr system is composed of an egr valve the opens vacuum from exhaust to intake manifold, a vacuum modulator that regulates the amount of vacuum introduced to the egr valve and finally the egr vsv (vacuum switching valve) solenoid that directs vacuum flow to the egr valve after a command from the ecm. A quick way to test this is to manually pump 3-4 inches of vacuum to the egr valve during idle and the engine should stall. This shows the egr valve is working. The modulator itself is nothing but a regulator valve that that reduces the engine vacuum from 18-19 inches to 3-4 inches needed by the egr valve. This modulator pressure can be checked by teeing a fitting and measured by a vacuum gage.
Finally, the vsv solenoid can be tested with an ohmmeter to check the resistance of the windings. However, it is reported that this part has a high attrition rate because of it's exposure to heat causing intermittent movement of the shaft inside. This is the part that should be checked thoroughly and replaced if possible.
Tuesday, May 5th, 2009 AT 10:39 PM