Heavy Duty

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.

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 Five Port (CVS5P):

COOLANT VACUUM SWITCH FIVE (5) PORT (CVS5P)

This valve can best be described as two separate valves. 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 vacuum to operate the EGR valve.

The second half of the switch behaves as a coolant vacuum switch three (3) port (CVS3P). This switch supplies manifold vacuum to the distributor at idle, ensuring full advance, until the engine coolant reaches 150°F. This part of the valve was added for cold weather driveability. Above 150°F, this switch relinquishes control over ignition advance to the thermal ignition delay control valve (TIDC).




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.