Chevrolet 1977 light duty truck, Service Manual

Page: 24 / 861

20 T H R O T T L E L I N K A G E
— Lubricate as covered in
Owner’s and Driver’s Manual. Check for dam­
aged or missing parts, interference or binding.
Any deficiencies should be corrected without
delay by a qualified mechanic.
21 UN DE R B OD Y —
Corrosive material used for ice and
snow removal and dust control can accumulate
on the underbody. If allowed to remain, these
materials can result in accelerated rusting and
deterioration of underbody components such as
fuel lines, frame and floor pan, exhaust system,
etc. At least once each year, preferably after a
winter’s exposure, these corrosive materials
should be removed by flushing the underbody
with plain water. Particular attention should be
given to cleaning out those areas where mud
and other foreign materials collect.
EMISSION CONTROL MAINTENANCE
NOTE: Additional recommended maintenance
instructions relating to vehicle use, evidence of
maintenance, and service replacement parts are
included in the New Vehicle Warranty Informa­
tion Folder.
22 C A R B U R E T O R C HOKE AND HOSES
- Check choke
mechanism for proper operation. Any binding
condition which may have developed due to
petroleum gum formation on the choke shaft or
from damage should be corrected. Check carbu­
retor choke hoses for proper connection, crack­
ing, abrasion or deterioration and correct or
replace as necessary.
23 ENGINE I DLE S P E E D A DJ US T ME N T
- Adjust engine
idle speed accurately (following the specifica­
tions shown on the label under the hood). Adjust­
ments must be made with test equipment known
to be accurate.
24
CARBURETOR MOUNTING-At designated intervals,
torque carburetor attaching bolts and/or nuts to
compensate for compression of gasket.
25 T H E R M O S T A T I C A L L Y C O N T R O L L E D AI R C L E A N E R -
Inspect installaticntomake certain that all hoses
and ducts are connected and correctly installed.
Also, check valve for proper operation.
26 M A N I F O L D H E A T V A L V E
-S o m e engines are
equipped with a manifold heat valve which
should be inspected and repaired as necessary
to insure free operation.
27 S P A R K PLUGS
— Replace at designated intervals
with type specified in Owner's and Driver’s
Manual.
28 ENGINE TIMING A DJ U S T ME N T & D I S T RI BU T O R C H E C K
—Adjust ignition timing following the specifica­
tions shown on label under the hood. Also, care­
fully inspect the interior and exterior of the dis­
tributor cap and rotorforcracks, carbon tracking
and terminal corrosion. Clean or replace as
necessary.
29 E X H A U S T GAS R E C I R C U L A T I O N S Y S T E M ( E G R )
- At
12 month/12,000 mile intervals, inspect and if
deposits exist, clean the EGR valve. Inspect the
EGR passages in the inlet manifold and clean as
required. A damaged EGR valve must be re­
paired or replaced. Check thermal switch for
proper operation. A malfunctioning switch must
be replaced. Check hoses for proper connection,
cracking, abrasions, or deterioration and re­
place as required.
30 C A R B U R E T O R F U E L I NL E T F I L T E R
- Replace filter
at designated intervals or if clogged.
31 ENGINE I DLE MI X T U R E —
At designated intervals or
in case of a major carburetor overhaul, or when
poor idle quality exists, adjust mixture by a me­
chanical method (lean drop), following the speci­
fications shown on the label under the hood.
32 T H R O T T L E R E T U R N C O N T R O L ( T R C ) S Y S T E M -
Check hoses for proper connections, cracking,
abrasion, or deterioration and replace as neces­
sary. Check for proper operation of system.
33 I DLE S TOP SOLENOID
- Check for proper oper­
ation. An inoperative solenoid must be replaced.
34 POS I TI VE C R A N K C A S E VENTI LAT I ON S YS TEM ( P C V )
— Check the PCV system for satisfactory oper­
ation at 12-month or 12,000-mile intervals. Re­
place the PCV valve at 24-month or 24,000-mile
intervals, blow out PCV valve hose with com­
pressed air and replace the filter. The PCV valve
should be replaced at 12-month or 12,000-mile
intervals when the vehicle is used in operations
involving heavy dust, extensive idling, trailer
pulling, and short trip use at freezing tempera­
tures where engine does not become thoroughly
warmed up. The PCV filter should be replaced at
12-month / 12,000-mile intervals under dusty
driving conditions.
35 EVAPORATI ON CO N T RO L S Y S T E M
(ECS)-Check all
fuel and vapor lines and hoses for proper con­
nections and correct routing as well as condi­
tion. Remove canisters and check for cracks or
damage. Replace damaged or deteriorated parts
as necessary. Replace filter in lower section of
canister. If vehicle is equipped with two canis­
ters, filter is located in lower canister only.
36 F U E L CAP, F U E L LI NES AND F U E L T A N K
-Inspect
the fuel tank, cap and lines for damage which
could cause leakage. Inspect fuel cap for correct
sealing ability and indications of physical dam­
age. Replace any damaged or malfunctioning
parts.
37 AI R C L E A N E R E L E ME N T
- Replace the engine air
cleaner element at designated intervals. Oper­
ation of vehicle in dusty areas will necessitate
more frequent element replacement. Your dealer
can be of assistance in determining the proper
replacement frequency for the conditions under
which you operate your vehicle.
CAUTION: Do not operate the engine without the
air cleaner unless temporary removal is neces­
sary during repair or maintenance of the vehicle.
When the air cleaner is removed, backfiring can
cause fire in the engine compartment.
38 S P A R K PLUG AND IGNITION COI L WI RE S
- Clean
exterior of wires; remove any evidence of corro­
sion on end terminals. Inspect spark plug and
ignition coil wires for evidence of checking,
burning, or cracking of exterior insulation and
tight fit at distributor cap and spark plugs, or
other deterioration. If corrosion cannot be re­
moved, or other conditions above are noted,
replace wire.