EGR Gas Flow Test

Use the following test procedure to determine if exhaust gas is flowing through the EGR valve. It can also be used to determine if the EGR tube is plugged, or the system passages in the intake or exhaust manifolds are plugged.

This is not to be used as a complete test of the EGR system.

The engine must be started, running and warmed to operating temperature for this test.

Typical EGR Valve:

1. All engines are equipped with two fittings located on the EGR valve. 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 at the vacuum motor fitting on the top of 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.
6. While applying vacuum, a minimum of 3 inches of vacuum, and with the engine running at idle speed, the idle speed should drop or the engine may even stall, if the vacuum is applied quickly. 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, or 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. Refer to EGR Valve Removal.
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 a plugged EGR tube or plugged passages at the intake or exhaust manifolds, refer to step (c). If the stem will not move, replace the EGR valve.

Note: The EGR valve, valve control and attaching hoses are serviced as one unit. Refer to EGR Valve Removal/Installation.

c. Remove the EGR tube between the intake and exhaust manifolds. Check and clean the EGR tube and its related openings on the manifolds. Refer to EGR Tube for procedures.
8. Do not attempt to clean the EGR valve. If the valve shows evidence of heavy carbon build-up near the base, replace it.