Vacuum Advance Control Systems; Four-Cylinder Engine System; Vacuum Advance Coolant Temperature Override (Cto) Valve - Jeep J-10 Series 1982 Technical & Service Manual

1G-30 IGNITION SYSTEMS
VACUUM ADVANCE
CONTROL SYSTEMS
Pigs
Four-Cylinder Engine System 1G-30
Six- ind Eight-Cylinder Engine System 1G-32
FOUR-CYLINDER ENGINE SYSTEM
Four-cylinder CJ engines use manifold vacuum for
distributor ignition advance. A delay valve maintains
the vacuum advance during sudden throttle openings
when the coolant temperature is below 120°F (49°C).
The delay valve is bypassed by the vacuum advance
coolant temperature override (CTO) valve when the cool
ant temperature is above 120°F (49°C). Refer to figure
1G-18 for a diagram of the system.
Vacuum Advance Coolant Temperature Override (CTO) Valve
The CTO valve is screwed into the thermostat housing
to allow the thermal sensor to be in contact with the
engine coolant. Depending on coolant temperature, the
CTO valve (fig. 1G-19) permits manifold vacuum with
the delay function or manifold vacuum without the de
lay function to control the distributor vacuum advance.
VACUUM
ADVANCE
MECHANISM
Pigs
16-35
Operation
When the engine coolant temperature is below 120°F
(49°C), manifold vacuum at port 1 is applied to port D. A
hose connects port D with the distributor vacuum ad
vance mechanism. The delay valve is in the circuit when
the valve is in this position.
When the engine coolant temperature reaches 120°F
(49°C), manifold vacuum at port 2 is also applied to port
D but the delay valve is bypassed. This may be consid
ered the normal operating mode. Refer to figure 1G-20.
Functional Test
(1) Disconnect vacuum hose from distributor vac
uum advance mechanism. Connect vacuum gauge to
vacuum hose.
TO CARB
BOWL VENT
90955
Rg. 16-18 Vacuum Advance Control System—Four-Cylinder Engines
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