Chevrolet Light Duty Truck 1973, Service Manual

Page: 507 / 979

E M I S S I O N C O N T R O L S Y S T E M S 6 T - 1 5
with the cold terminal; the time relay points are closed;
transmission switch points are open; idle stop solenoid is
de-energized and plunger retracted; vacuum advance
solenoid is de-energized with plunger shutting off the
port to vacuum advance unit.
When the ignition switch is turned on, the idle stop
solenoid is energized, extending the plunger to contact
the throttle lever. A circuit is completed from the
ignition switch through the vacuum advance solenoid
and to ground through the temperature switch. At the
same time another circuit is energized - this is from the
ignition switch through the time relay coil and to
ground, also as long as the relay points are closed, it
provides a path to ground for the vacuum solenoid (fig.
2
e).
With either one or both of the above circuits complete,
the vacuum solenoid is energized permitting vacuum
advance to the distributor.
In low gear operation, with engine temperature above 93
degrees, the temperature switch cold override points
open (fig. 3e). If 20 seconds have elapsed, the time relay
points are open also. This breaks the circuit(s) de­
energizing the vacuum advance solenoid, allowing the
plunger to block vacuum and open the advance unit to
atmosphere.
When the transmission is shifted into high forward gear,
the transmission switch points are closed by shift action
or by oil pressure as applicable. This completes the
circuit from the ignition switch through the transmission
switch to ground (fig. 4e). Vacuum advance solenoid is
energized.
COMPONENT DESCRIPTION
Idle Stop Solenoid
The idle stop solenoid (fig. 5e and
6
e) is a two position
electrically operated control, used to provide a
predetermined throttle setting. In the energized position
(plunger extended) the plunger contacts the carburetor
Fig. 2e—V8 TCS System (Cold Override Energized)
Fig. 3e—V8 TCS System (Low Gear Operation)
BATTERY
r
IGN. SWITCH
DIST. VACUUM
ADVANCE
UNIT
IDLE STOP SOLENOID
COLD
1
COLD OVERRIDE
SWITCH
TRANSMISSION
SWITCH (N.O.)
Energized
=
V.A.
De-energized = Atm.
^
9999
^
1
20 SECOND
TIME RELAY (N.C.)
Fig. 4e—V8 TCS System (High Gear Operation)
LIGHT DUTY TRUCK SERVICE MANUAL