Federal
SYSTEM OPERATION
The EGR system is an emission reducing system that concentrates primarily on the reduction of oxides of nitrogen (NOx). The purpose of the EGR system is accomplished by allowing a specified amount of hot exhaust gas to flow from the exhaust manifold into the intake manifold to mix with the incoming air/fuel mixture. This mixture enters the combustion chamber and lowers the peak flame temperature during combustion. This reduction in combustion temperature reduces the possibility of ignition knock and the level of NOx output.
This vehicle also uses a combination EGR/PHV solenoid to control the EGR and power heat control valve (PHV). When the engine is cold, less than 60°F (16°C), the EGR/PHV solenoid is open, thus allowing for vacuum to flow through the vacuum amplifier and activate the power heat control valve. Vacuum does not flow to the EGR valve because there is a vacuum bleed in the power heat control valve circuit, which yields an easier path for the vacuum to flow and does not allow the vacuum amplifier to amplify the signal. Once the engine reaches normal operating temperature, the EGR/PHV solenoid shuts off the source of vacuum to the power heat control valve. The vacuum is then forced to actuate the vacuum amplifier, which actuates the EGR control valve.
Charge Temperature Switch:
VENTURI VACUUM CONTROL SYSTEM
The EGR control valve is controlled by this system, venturi vacuum control. This system gets its vacuum control signal from a tap in the throat of the carburetor venturi. This control signal is very weak, so to compensate for this a vacuum amplifier is used to increase the vacuum to a level required to operate the EGR valve. To ensure that EGR is not occuring at wide open throttle, a dump diaphragm is used to compare venturi to manifold vacuum to determine when wide open throttle is achieved. At wide open throttle, the internal reservoir of vacuum is dumped, limiting the output to the EGR to manifold vacuum. The valves opening point is set at a higher vacuum than what the manifold could supply at wide open throttle, thus ensuring that the EGR could not be activated during wide open throttle.
As described earlier, the EGR system is disabled when the engine is below normal operating temperatures by the EGR/PHV solenoid. This solenoid is activated when the charge temperature switch senses that the air/fuel charge is above 60°F (16°C). Once this temperature has been reached, then the EGR delay timer will time out and the EGR valve will begin to operate.
Thermal Ignition Distributor Control (TIDC) Valve:
THERMAL IGNITION DISTRIBUTOR CONTROL VALVE (TIDC)
This valve is part of the EGR vacuum circuit (Refer to the Vehicle Emission Control Information Label) and gets manifold and ported vacuum from the CVS5P valve. This valve is used to direct manifold or ported vacuum to the distributor under specific engine temperature conditions.
Below 225 °F, the TIDC valve allows either manifold or ported vacuum, depending upon the position of the CVS5P valve, to flow to the distributor advance unit. Above 225 °F, the TIDC valve switches, shutting off any vacuum from the CVS5P (port 1), and allowing manifold vacuum to flow to the distributor vacuum advance (port d) from port 2. The full advance increases the engine RPM at idle, which increases the fan speed and cools the engine down while idling.
Coolant Vacuum Switch Cold Closed (CVSCC):
COOLANT VACUUM SWITCH COLD CLOSED (CVSCC)
The purpose of this valve is to keep vacuum from reaching the EGR control valve until the engine coolant reaches approximately 108 - 125°F. Once this temperature has been reached, then the valve opens allowing exhaust gases to recirculate.
EGR DELAY SYSTEM
The purpose of this system is to prevent exhaust gas recirculation for 60 seconds after the ignition is turned on. This system is composed of a vacuum delay valve and connecting vacuum hoses.