Jeep Wagoneer/Commando/Cherokee 1957-1983 Repair Information

Transmission Controlled Spark System

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DESCRIPTION AND OPERATION



The purpose of this system is to reduce the emission of oxides of nitrogen by lowering the peak combustion pressure and temperature during the power stroke.

The system incorporates the following components:

AMBIENT TEMPERATURE OVERRIDE SWITCH



This switch, located at the firewall, senses ambient temperatures and completes the electrical circuit from the battery to the solenoid vacuum valve when the ambient temperatures are above 63ºF.

SOLENOID VACUUM VALVE



See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: TCS electrical circuit

This valve is attached to the ignition coil bracket at the right side of the engine (V8 engines) or to a bracket at the rear of the intake manifold (sixes). When the valve is energized, carburetor vacuum is blocked off and the distributor vacuum line is vented to the atmosphere through a port in the valve, resulting in no vacuum advance. When the valve is deenergized, vacuum is applied to the distributor resulting in normal vacuum advance.

SOLENOID CONTROL SWITCH



This switch is located at the transmission valve body. It opens or closes in relation to car speed and gear range. When the transmission is in high gear, the switch opens and breaks the ground circuit to the solenoid vacuum valve. In lower gear ranges the switch closes and completes the ground circuit to the solenoid vacuum valve. With a manual transmission, the switch is operated by the transmission shifter shaft. With automatic transmissions, the switch is controlled by the speedometer gear speed. Under speeds of 25 mph the switch is activated.

COOLANT TEMPERATURE OVERRIDE SWITCH



See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: TCS hose routing

This switch is used only on the 304 V8. It is threaded into the thermostat housing. The switch reacts to coolant temperatures to route either intake manifold or carburetor vacuum to the distributor vacuum advance diaphragm.

When the coolant temperature is below 160ºF, intake manifold vacuum is applied through a hose connection to the distributor advance diaphragm, resulting in full vacuum advance.

When the coolant temperature is above 160ºF, intake manifold vacuum is blocked off and carburetor vacuum is then applied through the solenoid vacuum valve to the distributor advance diaphragm, resulting in decreased vacuum advance.

The relationship between distributor vacuum advance and the operation of the TCS system and coolant temperature override switch can be determined by referring to the emission control distributor vacuum application charts.

 
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