Chevrolet CHEVY VAN G10 SERIES Service Manual page 194

EMISSION C O N TR O L SYSTEM 6T-2
dieseling tendencies by allowing th e th ro ttle valve to close
beyond th e norm al idle position w hen the ignition is turned
off.
SYSTEM THEO RY
The TCS system com ponents are shown in their norm al at
rest position w ith the engine o ff and cold (Fig. 6T-1). The
tem perature sw itch p oints are closed, making con tact w ith the
cold term inal; the tim e relay points are closed, transm ission
sw itch points are open; CEC solenoid is de-energized, plunger
retracted and blocking d istrib utor vacuum advance and
opening d istributor vacuum advance u n it to atm osphere; idle
stop solenoid is de-energized w ith plunger retracted.
When the ignition sw itch is turn ed on the idle stop solenoid
is energized, extending the plunger to con tact the th ro ttle
lever. A circuit is com pleted from the ignition sw itch through
the CEC solenoid an d through the tem perature sw itch cold
term inal to ground. A t the same tim e an o th er circuit is
energized — this is from th e ignition switch through the tim e
(Cold Override & T im e Relay Energized)
relay coil and to ground, also as long as the relay points are
closed it provides a path to ground for the CEC solenoid (Fig.
6T-2). With either one or b o th o f th e above circuits com plete,
the CEC solenoid is energized; perm itting vacuum advance to
d istributor and, additionally, th e CEC solenoid plunger ex ­
tends, contacting the th ro ttle lever to provide deceleration
control at a preset value.
In low gear operation, w ith engine tem perature above 82
degrees, the tem perature switch cold override points open
(Fig. 6T-3). I f 20 seconds have elapsed the tim e relay points
are open also. This breaks the circuit(s) de-energizing the CEC
solenoid, allowing the plunger to block vacuum and open
advance u n it to atm osphere — deceleration control is no
longer effective, leaving th ro ttle co n tro l to be perform ed by
the idle stop solenoid.
When the transm ission is shifted in to high forw ard gear, the
transm ission sw itch points are closed by shift action or by oil
pressure as applicable (Fig. 6T-4). This com pletes the circuit
from the ignition switch through the CEC solenoid and
through the closed transm ission sw itch p oints to ground. The
CEC solenoid plunger is extended to provide deceleration
co n tro l and to open the vacuum p o rt to the advance u n it.
Fig. 6 T -4 —L-6 TC S System (High Gear Operation)
C H E V Y V A N S H O P M A N U A L