Battery And Battery Cable Service; Cooling System Inspection - GMC 4000 Series Service Manual

Sec. 6A
Page 260
GASOLINE ENGINES
are numbered consecutively from front to rear
and firing order is 1 -5 -3 -6 -2 -4 (fig. 8).
4. Refer to ENGINE ELECTRICAL (SEC. 6Y)
of this manual and inspect ignition distributor points,
rotor, and advance mechanism. Make necessary
parts replacement and/or adjustments.

BATTERY AND BATTERY CABLE SERVICE

1. Using battery hydrometer check specific
gravity of storage battery electrolyte in each cell.
Gravity reading below 1.230 (corrected to 80°F.)
indicates insufficient charge.
2. Use a voltmeter to check cranking voltage.
Disconnect coil primary lead from negative term ­
inal on coil to prevent engine from firing during
test.
3. With voltmeter connected between coil posi­
tive terminal and ground, operate starter. Voltage
of 9 volts or more when starter is cranking engine
indicates that battery, and ignition circuit to coil
are satisfactory. If voltage reading is le s s tan 9
volts when engine is being cranked, or if cranking
speed is low; a weak battery, defective starter
switch, or excessive resistance in ignition circuit
exists.
NOTE: If, when making check of cranking volt­
age, it is noted that cranking speed is uneven, this
is an indication of uneven cylinder compression,
defective starter or starter drive.
4. In cases where loose, corroded, or other­
wise defective battery cables and/or wiring are
found, the defects must be corrected to ensure
1 Air Cleaner
2 Ventilation Valve
3 Flame Arrestor
4 Vacuum Line
Figure 9 — Closed Positive Type Crankcase
Ventilation System on In-Line Engine
G M C S E R V I C E M A N U A L
5 Manifold Fitting
6 Intake Manifold
7 Rocker Arm Cover
8 Hose
T-3349
Figure 10— Typical Crankcase Ventilation
Valve for In-Line Engine
good engine performance.
5. If battery is weak or shows other evidence
of being defective, refer to appropriate coverage
in ENGINE ELECTRICAL (SEC.
for method of diagnosing battery deficiencies.
CHARGING CIRCUIT AND
WIRING INSPECTION
Refer to ENGINE ELECTRICAL (SEC. 6Y) in
this manual for procedure required to check per­
formance of charging circuit units.

COOLING SYSTEM INSPECTION

Refer to ENGINE COOLING SYSTEM (SEC.
6K) in this manual for arrangement of cooling
system units and for inspection and required main­
tenance procedures.
CARBURETOR THROTTLE
AND CHOKE LINKAGE
On most vehicles it will be necessary to re­
move air cleaner or air intake hose adapter at
carburetor to observe choke operation and action
of throttle linkage. All linkage must be maintained
in free working condition and should be checked as
part of tune-up procedure. Oil linkage pivot points
if any binding is evident. Complete information on
throttle linkage is given in ENGINE FUEL SYSTEM
(SEC. 6M) in this manual.
INSTRUMENT CHECK-OUT
1. Hook up test equipment for use in making
final adjustments. Equipment required consists of
dwell meter, tachometer, vacuum gauge and timing
light.
2. With engine running at idle speed, check
dwell angle and readjust if necessary.
3. With vacuum line to distributor disconnect­
ed and plugged, run engine at idle speed and check
ignition timing with timing light. Loosen distrib­
utor clamp and rotate distributor body to change
timing as required. Tighten distributor clamp and
connect the vacuum line after checking timing.
6Y) this
in m anual