System Description

Fig. 8 Dual EGR Control Solenoid:

Fig. 10 EGR Valve & Position Sensor:

Fig. 11 EGR system schematic:

This system consists of an EGR valve/sensor assembly, Figs. 10, a dual EGR control solenoid and EGR cooler assembly, Fig. 11. The EGR gas flow is controlled by the ECA, which uses engine manifold vacuum to operate the EGR valve.

The EGR valve is attached to the intake manifold under the carburetor. The valve controls the flow of gases through a tapered pintle valve and seat. A position sensor attached to the valve provides an electrical signal to the ECA which indicates EGR valve position.

The EGR valve used in this system is completely covered, and no pintle movement can be seen when the valve is installed. The valve and position sensor are serviced as individual units.

The EGR valve flow rate is controlled by dual EGR control solenoids mounted on a bracket attached to the lefthand valve cover, Fig. 8. Proper control of the vacuum used to operate the EGR valve requires two types of solenoid valves: a vent valve which is normally open, in which the outlet port is normally connected to the inlet port when the solenoid is not operated; a vacuum valve which is normally open, in which the outlet port is normally blocked when the solenoid is not operated.

In order to provide improved flow characteristics, better engine operation and EGR valve durability, an external EGR gas cooler, Fig. 11, is used to reduce exhaust gas temperature. The cooler assembly is mounted over the right valve cover and uses engine coolant to reduce the temperature of exhaust gases routed from the exhaust manifold to the EGR valve.

During operation, the EGR valve is operated by vacuum supplied from the intake manifold. The vacuum and vent solenoids function together, as determined by the ECA to:

1. Increase EGR flow by applying vacuum to the EGR valve.
2. Maintain EGR flow by trapping vacuum in the system.
3. Decrease EGR flow by venting the system to atmosphere.

With information received from the various sensors, the ECA determines the correct amount of EGR flow required, checks the position of the EGR valve pintle, and determines if a change in position is required. In response to these calculations, the ECA puts the EGR system into one of the modes mentioned previously. The ECA samples and calculates these changes about ten times each second, for improved fuel economy and driveability under all conditions.