In order to reduce the emission of oxides of nitrogen (NO x ), exhaust gases are ducted from the intake manifold crossover passage to dilute (with inert, oxygen-free gas) the fuel/air mixture. Most engines use an EGR control valve. This valve directs exhaust gas from the crossover passage into the intake manifold. By using either ported-vacuum (varies with throttle opening) or venturi-vacuum signals, the EGR valve is able to proportion the exhaust gas flow to the amount of vacuum present in the carburetor. Thermal switches on the engine and radiator prevent recirculation during engine warmup. All models have a delay timer relay and a solenoid valve to shut off vacuum to the system until the engine has run 30-40 seconds after startup.
Air temperature should be above 68°F for this test.
- Check all of the vacuum hoses which run between the carburetor, intake manifold, EGR valve, and the vacuum amplifier (if so equipped). Replace the hoses and tighten the connections, as required.
- Allow the engine to warm up. Connect a tachometer to it. Start with the engine idling in neutral and rapidly increase the engine speed to 2,000 rpm.
- If the EGR valve stem moves (watch the groove on the stem), the valve and the rest of the system are functioning properly. If the stem does not move, proceed with the rest of the EGR system tests.
- Disconnect the vacuum supply hose from the EGR valve. Apply a vacuum of at least 10 in. Hg to the valve with the engine warmed-up and idling and the transmission in Neutral.
A source of more than adequate vacuum is the intake manifold vacuum connection. Run a hose from the EGR valve directly to the connection.
- When vacuum is applied to the EGR valve, the engine speed should drop at least 150 rpm. In some cases the engine may even stall. If the engine does not slow down the EGR valve does not operate, the valve is defective or dirty. Replace it or remove the deposits from it.
Always replace the EGR valve gasket when the valve is removed for service, even if the valve itself is not replaced.
- If the EGR valve is functioning properly, reconnect its vacuum line and test the temperature control valve.
- Test the EGR system coolant temperature operated control valve for leaks. The valve is located on either the right or left-side of the radiator top tank.
- Disconnect the vacuum hose from the EGR coolant temperature operated control valve, then connect a vacuum source and gauge to the valve fitting, in place of the hose.
- Apply 10 in. Hg of vacuum to the valve. If the valve loses more than 1 in. Hg in one minute, the valve is defective and must be replaced.
- If everything else is functioning properly, the EGR system does not work and the engine is equipped with a vacuum amplifier, the amplifier is at fault. Replace it and repeat the system test.
Before replacing the amplifier, check the vacuum port in the carburetor. If it is clogged, clean it with solvent; do not use a drill.EGR Delay System
- Unfasten the distributor-to-coil lead.
- Disconnect the vacuum line which runs from the delay solenoid to the vacuum amplifier at the amplifier end.
- Turn the car's ignition switch to START and then release it, so that it returns to RUN .
- Suck on the end of the disconnected hose; the hose should be blocked.
- After about 35 seconds from the time that the ignition switch was turned to START , the solenoid should open, allowing air to flow through the line.
- If the system isn't working, disconnect the solenoid and connect it directly to a 12-volt power source, making and breaking the circuit several times. If the solenoid works, replace the delay timer.
- If the solenoid doesn't work, replace the solenoid.
- Reconnect the vacuum lines and the coil after completing the test.
EGR REMINDER LIGHT
This light is designed to remind the driver that regularly scheduled service is due; it does not mean that the EGR system is not working properly. This system is only used on cars without a catalytic converter.
- After checking the EGR system for proper operation, slide the rubber boot on the EGR reminder odometer up, out of the way.
- Reset the odometer with a small screwdriver.
- Slide the boot back down over the odometer. The light will come on again when the next 15,000 mile check-up is due.
REMOVAL & INSTALLATION
- Allow the engine to cool.
- Remove the air cleaner housing.
- It may be necessary to label the EGR valve vacuum hose to avoid confusing it with a hose for the air cleaner.
- Disconnect the vacuum hose, then remove the mounting fasteners. Typically 6-cylinder engines use mounting nuts, while 8-cylinder engines use bolts.
- Remove tha valve from the manifold.
- Installation is the reverse of the removal procedure. Always use a new gasket when installing the valve and anti-seize compound on the fastener threads.