Wrangler L4-150 2.5L VIN H TBI (1986)
Thermal Vacuum Valve: Description and Operation
Fig. 23 Spark CTO valve
SPARK COOLANT TEMPERATURE OVERRIDE (CTO) VALVE
The spark CTO valve, Fig. 23, is screwed into the thermostat housing so that the thermal sensor is in contact with the engine coolant. The CTO valve
controls the distributor vacuum advance according to coolant temperature by permitting manifold vacuum with or without the delay function.
When coolant temperature is below 120° F, manifold vacuum at port 1 is applied to port D. Port D is connected to the distributor spark advance
mechanism with a vacuum hose. When the valve is in this position, the delay valve is in the circuit.
When coolant temperature reaches 120° F, manifold vacuum at port 2 is also supplied to port D, but the delay valve is bypassed. This is the normal
operating condition.
Fig. 24 Vacuum spark control delay valve
VACUUM SPARK CONTROL DELAY VALVE
This valve is used in the vacuum advance circuit to provide improved driveability when the engine is cold, Fig. 24.
Ports 1 and 2 and ports 3 and 4 of this valve are connected internally. When vacuum is greater at port 4 then at port 1 (such as during sudden
acceleration), air must flow through the orifice to equalize pressure. This creates a momentary delay that prevents a sudden decrease in spark advance.
When vacuum is greater at port 1 than at port 4, air flows freely through the unseated check valve and the pressure is instantly equalized.
COOLANT TEMPERATURE OVER RIDE (CTO) VALVE-STANDARD COOLING SYSTEM
