Chevrolet 10 Series 1970, Руководство по обслуживанию

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SECTION 6T
EMISSION CONTROL SYSTEMS
CONTENTS OF THIS SECTION
Page Page
Positive Crankcase V en tila tion ......................................................... 6T-1 Transmission C ontrolled S p a r k ......................................................... 6T-1
C ontrolled Com bustion System ...................................................... 6T-1 A ir Injection Reactor S y s t e m ........................................................... 6T-3
Evaporation Emission Control ......................................................... 6T-1
POSITIVE CRANKCASE VENTILATION
T h is system re m o v e s engine crankcase vapors which
resu lt fro m norm al engine combustion. They are r e ­
m oved by u tilizin g the m anifold vacuum to draw o ff the
vapors through a m etered P .C .V . va lve and ultim ately
to the intake system fo r engine reburn. R e fe r to Section
0 fo r s e rv ic e requirem ent o f this valve.
CONTROLLED COMBUSTION SYSTEM
T h is system in crea ses combustion efficie n cy through
lea n er carbu retor adjustments and r e v is e d distributor
calibration. In addition, on the m a jo rity o f installations,
sp ecia l th erm ostatically controlled a ir clean ers are used
to maintain hotter intake a ir (100 °F o r above) to lean the
carbu retor. R e fe r to Section 0 fo r A ir C leaner Care
recom m endations.
EVAPORATION EMISSION CONTROL
T h is system is designed to reduce fuel vapor em ission
that norm ally vents to the atm osphere from the gasoline
tank and carbu retor fuel bowl. The a ir cleaner filte r
mounted at the bottom o f the canister re q u ire s rem oving,
cleaning and oilin g at 12,000 m ile in terva ls. A ll other
parts a re s e rvic e d as a com plete replacem ent as outlined
in Section 8.
TRANSMISSION CONTROLLED SPARK
The distributor vacuum advance has been elim inated
in the low forw ard ge a rs as is shown on the chart at the
bottom o f the schem atic diagram o f the system (F ig . 1).
The control o f the vacuum advance is accom plished by
means o f a solenoid vacuum switch which is en ergized
in the low g ea rs by grounding a switch at the tra n s­
m ission . When the solenoid is en ergized , the vacuum
source to the d istribu tor is shut o ff and the vacuum
advance unit is vented to the atm osphere by means o f
a clean a ir connection to the ca rb u retor a ir hose. T h is
p reven ts the vacuum advance unit fro m becom ing vacuum
locked at some advance position.
The T.C .S . System also in corp orates a tem perature
o v e r r id e system which p rovid es full vacuum in a ll g ea rs
when the engine is cold fo r im proved d riva b ility . A
therm ostatic w ater tem perature switch p ro vid es the s ig ­
nal which en e rg ize s a norm ally closed rela y, opening the
c irc u it to the solenoid vacuum switch, thus providing
full vacuum. Some v eh icles also have a hot o v e rrid e
switch which p rovid es full vacuum to im prove engine
cooling.
The system may be checked fo r p ro p er function by
connecting a vacuum gage in the hose between the s o le ­
noid and the distribu tor. Full vacuum should be obtained
when the transm ission is in the gear as indicated on
above chart when the engine is warm and running.
If full vacuum is found in all gears, the cause may be:
1. Fuse blown
2. W ire disconnected at solenoid
3. W ire disconnected at transm ission switch
4. T ran sm ission switch fa iled
5. Tem perature o v e rrid e switch en erg ized - check by
disconnecting e le c tr ic a l lead
6. Solenoid fa iled
If no vacuum is found in high g ear, the cause may be:
1. Clean a ir line and distributor vacuum line re v e rs e d
at solenoid
2. Foreign m ateria l in solenoid
3. Plunger return spring broken
4. D istributor o r m anifold vacuum hose broken or
disconnected
5. T ran sm ission switch o r w ire shorted to ground.
NOTE: Six cylin d er synchrom esh engines in
third gear do not have full vacuum at idle b e ­
cause of the ported spark. Autom atic tran sm is­
sion veh icles w ill not show vacuum until they
are driven to p e rm it transm ission to upshift
into high gear.
CHEVROLET TRUCK SERVICE MANUAL