Chevrolet CHEVY VAN G10 SERIES Service Manual page 200

EMISSION CON TR O L SYSTEM 6T-8
Fig. 6 T -1 4 -S m a ll V 8 TCS System
(High Gear Delay Relay)
In low gear o peratio n, w ith engine tem perature above 82
degrees, the tem perature sw itch cold override p oin ts open
(Fig. 6T-13). This breaks the circuit from the vacuum sole­
noid, allowing the plunger to block vacuum and open the
advance u nit to atm osphere.
When the transm ission is shifted into high forw ard gear, the
transm ission sw itch points are closed by shift action or by oil
pressure as applicable. This com pletes the circuit from the
ignition sw itch through the delay relay tim ing circuit and
th ro u g h the transm ission sw itch to ground (Fig. 6T-14).
V acuum advance solenoid is n o t energized.
A fter a delay o f 23 seconds (in high gear) the delay relay
points close, com pleting the circuit through the vacuum
advance solenoid to ground (Fig. 6T-15). V acuum advance to
the d istributor is perm itted by energizing the solenoid. Subse­
q u en t in te rru p tio n o f the high gear position will result in a 23
second delay before the vacuum advance solenoid is energized
again.
Fig. 6 T -1 5 —Small V 8 TCS System
(High Gear Operation)
Fig. 6 T -1 6 —Small V 8 Idle Stop Solenoid
COMPONENT DESCRIPTION
Idle Stop Solenoid
T he idle stop solenoid (Fig. 6T-16) is a tw o position
electrically o perated con tro l, used to provide a predeterm ined
th ro ttle setting. In the energized position (plunger extended)
the plunger contacts the carburetor th ro ttle lever an d prevents
full closing o f th e carb u reto r th ro ttle plates. This fast idle
co n tro l w hen de-energized (plunger retracted ) allows th ro ttle
plates to close b ey o n d the norm al idle position; thereby
shutting o ff air supply and in essence starving the engine so
th at it will shut dow n w ith o u t dieseling. The idle stop solenoid
is bracket-attached to the carburetor so th a t the plunger, when
ex tended, contacts the th ro ttle lever.
Fig. 6 T -1 7 —Small V 8 Vacuum Advance Solenoid
C H E V Y V A N S H O P M A N U A L