EGR Gas Flow Test

1 The EGR valve has 2 fittings. The upper fitting, located on the vacuum motor, supplies engine vacuum to a diaphragm within the EGR valve for valve operation. The lower fitting, located on the base of the EGR valve, is used to supply exhaust back-pressure to the EGR valve control.
2. Disconnect the rubber hose from the upper fitting on the EGR valve vacuum motor.
3. Connect a hand-held vacuum pump to this fitting.
4. Start the engine.
5. Slowly apply 5 inches of vacuum to the fitting on the EGR valve motor. Engine speed should begin to drop when applied vacuum reaches 2.0 to 3.5 inches Hg.
6. While applying vacuum, and with the engine running at idle speed, the idle speed should drop or the engine may even stall. This is indicating that exhaust gas is flowing through the EGR tube between the intake and exhaust manifolds.
7. If the engine speed did not change, the EGR valve may be defective, the EGR tube may be plugged with carbon, or the passages in the intake and exhaust manifolds may be plugged with carbon.
a. Remove EGR valve from engine.
b. Apply vacuum to the vacuum motor fitting and observe the stem on the EGR valve. If the stem is moving, it can be assumed that the EGR valve is functioning correctly The problem is in either the EGR tube or the passages at the intake or exhaust manifolds. Check these passages and clean if necessary.
c. Remove the EGR tube between the intake manifold and cylinder head. Check and clean the EGR tube and its related openings on the manifolds.