Chevrolet 10 Series 1970 Service Manual page 385

EMISSION CONTROL SYSTEMS
Positive Crankcase V en tilation .........................................................
C ontrolled Com bustion System
Evaporation Emission Control .........................................................
POSITIVE CRANKCASE VENTILATION
Th is system rem o ves engine crankcase vapors which
resu lt from norm al engine combustion.
m oved by u tilizing the manifold vacuum to draw o ff the
CONTROLLED COMBUSTION SYSTEM
Th is system in crea ses combustion efficien cy through
lean er carburetor adjustments and re v is e d distributor
calibration. In addition, on the m ajority o f installations,
sp ecia l th erm ostatically controlled a ir clean ers are used
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 carburetor fuel bowl.
mounted at the bottom o f the canister req u ires rem oving,
TRANSMISSION CONTROLLED SPARK
The distributor vacuum advance has been elim inated
in the low forw ard gea 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 gea rs by grounding a switch at the tran s­
m ission. When the solenoid is en ergized, the vacuum
source to the d istributor 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 carbu retor a ir hose. T his
prevents 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 rrid e system which p rovid es full vacuum in all gea rs
when the engine is cold fo r im proved d riva b ility.
therm ostatic w ater tem perature switch provides 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 veh icles also have a hot o v e rrid e
switch which provid es full vacuum to im prove engine
cooling.
The system may be checked fo r p roper function by
connecting a vacuum gage in the hose between the s o le ­
noid and the distributor.
SECTION 6T
CONTENTS OF THIS SECTION
......................................................
They are r e ­
The a ir cleaner filte r
Full vacuum should be obtained
Page
6T-1 Transmission C ontrolled S p a r k .........................................................
6T-1 A ir Injection Reactor S y s t e m ...........................................................
6T-1
vapors through a m etered P .C .V . valve 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.
to maintain hotter intake a ir (100 °F or above) to lean the
carburetor. R e fe r to Section 0 fo r A ir
recom m endations.
cleaning and oiling at 12,000 m ile in terva ls. A ll other
parts are serviced as a com plete replacem ent as outlined
in Section 8.
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 ransm ission switch failed
5. Tem perature o v e rrid e switch en ergized - check by
disconnecting e le c tric a l lead
6. Solenoid failed
If no vacuum is found in high gear, the cause may be:
1. Clean a ir line and distributor vacuum line re v e rs e d
at solenoid
2. Foreign m aterial in solenoid
A 3. Plunger return spring broken
4. D istributor o r
disconnected
5. Transm ission
NOTE: Six
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 erm it transm ission to upshift
into high gear.
C leaner Care
m anifold vacuum hose
switch o r w ire shorted to ground.
cylin d er synchromesh engines in
CHEVROLET TRUCK SERVICE MANUAL
Page
6T-1
6T-3
broken or