Chevrolet Light Duty Truck 1973, Service Manual

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Fig. 20—Cooling System Pressure Check
LIGHT DUTY TRUCK SERVICE MANUAL
Ignition Switch
With voltmeter connected as described for the Cranking
Voltage Test, turn ignition switch to ON. Voltage should
drop to 5 to 7 volts as current is now passing through
high resistance wire connected between ignition switch
and ( + ) positive terminal of coil. If battery voltage of 12
volts is obtained, the starter solenoid is by-passing the
high resistance wire connected between ignition switch
and (+ ) positive terminal of coil, thus the starter
solenoid is not functioning properly to by-pass the
ignition resistance wire or the ignition circuit is
incorrectly wired.
NOTE: The voltage drop (12 to 5-7 volts) will
only take place when the points are closed. If
the points are open, the path through the
resistance wire will not be completed.
Distributor Resistance
Use equipment as directed by manufacturer. Excessive
resistance in primary circuit must be eliminated before
continuing with test procedure.
Secondary Resistance
Use equipment as directed by manufacturer.
• Uniform “normal readings” as specified by
manufacturer indicate all secondary circuit compo­
nents are in good condition.
• If all readings are “below normal”, check for
corroded coil tower terminal, poorly connected or
broken coil wire, center cap electrode or rotor tip
burned, or an open secondary in coil.
• If readings are “higher than normal” at two or
more plugs adjacent in firing order, cross firing is
• Secondary Resistance
• Ignitioft’oulput and secondary leakage
Cranking Voltage (Fig. 19)
1. Disconnect coil .primary lead at the coil negative
terminal , to prevent engine from firing during
cranking.
\
2. Connect voltmeter between primary terminal of coil
(resistance wire side) and ground.
3. Operate starting mbtor.
a. If voltage is 9 volts or more and cranking speed
is satisfactory, the battery, starter, cables, starter
switch and ignition circuit to coil (by-passing
resistance wire) are in good condition.
\
b. If below 9 volts, check circuit until difficulty is
located.
Meter reading below specification-W eak
battery;
defective cables^ connections, switch or starter;
defective ignition circuit to coil.
Cranking speed below norm al-Excessive
resistance
in cables or starting motor; excessive mechanical
drag in engine.
Uneven cranking sp«ec£-
Uneven compression,
defective starter to starter drive.
6 -1 2 ENQINE
Fig. 19-Testing Cranking Voltage