This system reduces the amount of oxides of nitrogen in the exhaust by allowing a predetermined amount of hot exhaust gases to recirculate and dilute the incoming fuel/air mixture. The principal components of the system are the EGR valve and the Coolant Control Exhaust Gas Recirculation (CCEGR) valve. The former is located in the intake manifold and directly regulates the flow of exhaust gases into the intake. The latter is located in the thermostat housing and overrides the EGR valve when coolant temperature is below 125°F (52°C).
Ported vacuum uses a slot in the carburetor throttle body which is exposed to an increasing percentage of manifold vacuum as the throttle opens. The throttle bore port is connected to the EGR valve. The flow rate of recirculation is dependent on manifold vacuum, throttle position and exhaust gas back pressure. Recycling at wide open throttle is eliminated, by calibrating the valve opening point above the manifold vacuum available at wide open throttle, which provides maximum performance.
- Inspect all hose connections between the carburetor, intake manifold and EGR valve.
- Check the valve with the engine warmed and running.
- Allow the engine to idle in Neutral for 70 seconds, with the throttle closed. Abruptly accelerate the engine to about 2000 rpm, but not more than 3000 rpm.
- Visible movement of the EGR valve stem should occur during this operation. Movement can be seen by the position of the groove on the EGR valve stem. You may have to repeat the operation several times to definitely ascertain movement.
Inspect the EGR valve for deposits, particularly around the poppet and seat area. If deposits amount to more than a thin film, the valve should be cleaned. Apply a liberal amount of manifold heat control valve solvent to the poppet and seat area and allow the deposits to soften. Open the valve with an external vacuum source and remove the deposits, with a suitable sharp tool.
An alternate procedure to this messy operation is to simply replace the valve if it is extremely clogged.
Coolant Control Exhaust Gas Recirculation (CCEGR) Valve
This valve is mounted in the thermostat housing and is color coded yellow.
- Remove the vacuum connection to the sensor.
- Remove the valve from the housing.
- Place it in an ice bath below 40°F (4°C) so that the threaded portion of the valve is covered.
- Connect a hand vacuum pump to the valve nipple corresponding to the yellow stripe hose. Apply 10 in. Hg (34 kPa) of vacuum. There should be no more than 1 in. Hg (3 kPa) drop in vacuum in 1 minute. If the vacuum reading falls off, the valve should be replaced.
REMOVAL & INSTALLATION
- Disconnect the vacuum line to the EGR valve. Inspect for damage.
- Remove the EGR valve bolts from the intake manifold.
- Remove the EGR valve from the intake manifold.
- Clean the gasket surfaces, then discard the old gasket. Check for any signs of leakage or cracked surfaces.
- Assemble the EGR valve with a new gasket onto the intake manifold.
- Insert the mounting screws, then tighten them to 17 ft. lbs. (22 Nm).
- Connect the vacuum lines to the EGR valve.
- Disconnect the vacuum hose from the valve.
- Using an appropriate sized wrench, remove the valve from the housing.
- Installation is the reverse of removal. Use a non-hardening sealer on the threads and tighten until snug.