See Figures 1, 2, 3, 4 and 5
Exhaust gas recirculation is used to reduce combustion temperatures in the engine, thereby reducing the oxides of nitrogen emissions.
An EGR valve is mounted on the center of the intake manifold. The recycled exhaust gas is drawn into the bottom of the intake manifold riser portion through the exhaust manifold heat stove and EGR valve. A vacuum diaphragm is connected to a timed signal port at the carburetor flange.
As the throttle valve is opened, vacuum is applied to the EGR valve vacuum diaphragm. When the vacuum reaches about 2 in. Hg, the diaphragm moves against string pressure and is in a fully up position at 8 in. Hg of vacuum. As the diaphragm moves up, it opens the exhaust gas metering valve which allows exhaust gas to be pulled into the engine intake manifold. The system does not operate when the engine is idling because the exhaust gas recirculation would cause a rough idle.
On some later models, a thermal vacuum valve inserted in the engine thermostat housing controls the application of the vacuum to the EGR valve. When the engine coolant reaches a predetermined temperature, the thermal vacuum valve opens and allows vacuum to be routed to the EGR valve. Below the predetermined temperature, the thermal vacuum valve closes and blocks vacuum to the EGR valve.
Most vehicles have a B.P.T. valve installed between the EGR valve and the thermal vacuum valve. The B.P.T. valve has a diaphragm which is raised or lowered by exhaust back pressure. The diaphragm opens or closes an air bleed, which is connected into the EGR vacuum line. High pressure results in higher levels of EGR, because the diaphragm is raised, closing off the air bleed, which allows more vacuum to reach and open the EGR valve. Thus the amount of recirculated exhaust gas varies with exhaust pressure.
Some early models use a V.V.T. valve (venturi vacuum transducer valve) instead of the B.P.T. valve. The V.V.T. valve monitors exhaust pressure and carburetor vacuum in order to activate the diaphragm which controls the throttle vacuum applied to the EGR control valve. This system expands the operating range of the EGR flow rate as compared to the B.P.T. unit.
See Figures 6 through 11
A quick service check for the EGR valve operation is with the engine running at idle, push up on the EGR control valve diaphragm with your finger. When this is done, the engine idle should become rough and uneven.
- Remove the EGR valve and apply enough vacuum to the diaphragm to open the valve.
- The valve should remain open for over 30 seconds after the vacuum is removed.
- Check the valve for damage, such as warpage, cracks, and excessive wear around the valve and seat.
- Clean the seat with a brush and compressed air and remove any deposits from around the valve and port (seat).
- To check the operation of the thermal vacuum valve, remove the valve from the engine and apply vacuum to the ports of the valve. The valve should not allow vacuum to pass.
- Place the valve in a container of water with a thermometer and heat the water. When the temperature of the water reaches 134-145°F (57-63°C), remove the valve and apply vacuum to the ports. The valve should allow vacuum to pass through it.
- To test the B.P.T. valve, disconnect the two vacuum hoses from the valve. Plug one of the ports. While applying pressure to the bottom of the valve, apply vacuum to the unplugged port and check for leakage. If any exists, replace the valve.
- To test the check valve, remove the valve and blow into the side which connects the EGR valve. Air should flow. When air is supplied to the other side, air flow resistance should be greater. If not, replace the valve.
- To check the V.V.T. valve disconnect the top and bottom center hoses and apply a vacuum to the top hose. Check for leaks. If a leak is present, replace the valve.
REMOVAL & INSTALLATION
EGR Control Valve
- Remove the nuts which attach the EGR tube and/or the BP tube to the EGR valve (if so equipped).
- Unscrew the mounting bolts and remove the heat shield plate from the EGR control valve (if so equipped).
- Tag and disconnect the EGR vacuum hose(s).
- Unscrew the mounting bolts and remove the EGR control valve.
- Install the EGR valve assembly with mounting bolts (torque retaining bolts EVENLY) to intake manifold location.
- Connect all vacuum hoses and install the heat shield if so equipped.
- Connect EGR tube or BP tube to the EGR valve if so equipped. If replacing the EGR valve assembly always be sure that the new valve is identical to the old one.