California

NOTE: Heavy Duty - GVW 8501 lbs and over.
Light Duty - GVW 8500 lbs and under.


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.


VENTURI VACUUM CONTROL SYSTEM

The EGR control valve is controlled by this system of 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.

Coolant Vacuum Switch Five Port (CVS5P):

COOLANT VACUUM SWITCH FIVE (5) PORT (CVS5P)

This switch can best be described as two separate switches. One half of the switch acts like a two port coolant controlled engine vacuum switch (CCEVS). This switch is a normally closed switch up to 150°F, above this temperature, the switch opens allowing ported vacuum to operate the EGR valve.

The second half of the switch behaves as a coolant vacuum switch three (3) port (CVS3P). Below 150 °F, this switch supplies manifold vacuum to the distributor, via the TIDC valve, ensuring full advance at idle. Above 150°F, the CVS3P switches to allow ported vacuum to flow to the distributor through the TIDC valve.

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.




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.