Chevrolet CHEVY VAN G10 SERIES Service Manual page 193

EMISSION CONTROL SYSTEMS
Positive Crankcase V e n tila tio n ...............................................6T-1
C ontrolled C om bustion S y s t e m ............................................ 6T -1
Evaporation Emission C o n t r o l ...............................................6T-1
POSITIVE CRANKCASE VENTILATION
This system removes engine crankcase vapors w hich result
from norm al engine com bustion. T hey are rem oved by utiliz­
ing the m anifold vacuum to draw o ff the vapors through a
CONTROLLED COMBUSTION SYSTEM
This system increases com bustion efficiency through leaner
carburetor adjustm ents and revised d istributor calibration. In
ad dition, on th e m ajority o f installations, special th erm o ­
EVAPORATION EMISSION CONTROL
This system is designed to reduce fuel vapor em ission th at
norm ally vents to th e atm osphere from the gasoline tan k and
carb uretor fuel bow l. The air cleaner filter m ou nted at the
TRA N SM ISSIO N CO N TRO LLED SP A R K SYSTEM
C ontrol o f exhaust em ission em itted by vehicles using the
six-cylinder engine, is accom plished by preventing ignition
vacuum advance w hen the vehicle is operating in low forw ard
gears.
V acuum advance is controlled by a solenoid-operated valve,
w hich is energized by grounding a norm ally open sw itch at the
transm ission. When th e solenoid is in the non-energized posi­
tion , vacuum to the d istributor advance u n it is shut o ff and
the distributor is vented to atm osphere through a filter at the
opposite end o f the solenoid — venting the d istrib u tor ad­
vance u nit prevents it from becom ing locked at an advanced
position. When the solenoid is energized, the vacuum p o rt is
uncovered and the plunger is seated a t the opposite end,
shutting off the clean air vent. High gear deceleration th ro ttle
blade setting is perform ed w ith the solenoid de-energized.
SECTION 6T
INDEX
Page
Transmission C ontrolled Spark System ..............................6T -1
Air Injection R eactor S y s te m .................................................6 T -1 2
m etered P.C.V. valve and ultim ately to th e intake system for
engine reburn. Refer to Section 0 for service requirem ent of
this valve.
statically co n trolled air cleaners are used to m aintain h o tte r
intake air (1 0 0 °F or above) to lean the carburetor. Refer to
Section 0 for air cleaner care recom m endations.
b o tto m o f the canister' requires replacem ent at intervals spec­
ified in Section 0. All other parts are serviced as a com plete
replacem ent as outlined in Section
SIX CYLINDER ENGINE
GENERAL DESCRIPTION
T he CEC solenoid is controlled by tw o sw itches and a tim e
relay. The solenoid is energized in th e high forw ard gear and in
reverse on H ydra-m atic by a transm ission o p erated switch. A
therm ostatic co olant tem perature sw itch is used to provide
therm al override below 82° F. The tim e relay is incorp orated in
the circuit to energize the CEC valve for 20 seconds after the
ignition key is tu rn ed on. T he relay 20 second delay begins
w hen the ignition key is tu rn ed on, b u t the solenoid will
rem ain energized as long as coolant tem perature is below
82°F .
Wider th ro ttle blade openings at idle are required to
com pensate for the retard ed spark co nd ition produced by the
design o f th e em ission reduction system . T o prevent engine
dieseling at engine shut dow n, an idle stop solenoid is p ro ­
vided. The ignition activated idle stop solenoid eliminates
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C H E V Y V A N SH O P M A N U A L