Chevrolet 1977 light duty truck, Руководство по обслуживанию

Страница: 634 / 861

DIAGNOSIS
N O C R A N K I N G A C T I O N
1. Make sure that control lever is neutral (N) or park
(P) position or that clutch pedal is depressed on manual
transmission.
2. M ake quick check o f battery and cables. If battery is
low, the solenoid usually will produce a clattering noise,
ecause a nearly discharged battery will not sustain the
8ltage required to hold solenoid plunger in after solenoid
switch as been closed.
3. If starter m otor spins and drive pinion engages ring
gear but does not drive it, overrunning clutch is slipping.
Remove m otor to replace drive assembly.
4. If starter m otor does not operate, note whether
solenoid plunger is pulled into solenoid when solenoid curcuit
is closed. Ordinarily the plunger makes a loud click when it
is pulled in. If plunger is pulled in, solenoid circuit is okay
and trouble is in solenoid switch, cranking m otor, or cranking
m otor circuit. The starter m otor m ust be removed for repairs
to switch or motor.
5. If plunger does not pull into solenoid when ignition
switch is turned to "STA R T", the solenoid circuit is open,
or solenoid is at fault.
6. To find reason why plunger does not pull into
solenoid, connect jum per between solenoid battery terminal
and term inal on solenoid switch to which purple wire is
connected. If cranking m otor operates, solenoid is okay;
trouble is in ignition switch, neutral start switch, or in wires
and connections between these units.
7. If starter m otor still does not operate, remove m otor
for inspection and test of solenoid switch.
C R A N K I N G S P E E D A B N O R M A L L Y L O W
Abnormally low cranking speed may be caused by low
battery or defective cables, defective solenoid switch,
defective cranking m otor, or an internal condition of engine.
1. M ake quick check of battery. If low battery is
indicated, test battery. If defective cables are indicated, test
cables.
NOTE: Check generator belt tension for cause of low
battery.
2. If battery and cables are okay, test cranking m otor
and solenoid switch.
3. If starter m otor and solenoid switch test okay, the
trouble is due to an internal condition of engine. This may
be due to use of engine oil which is too heavy for prevailing
tem peratures.
V O L T A G E T E S T OF S T A R T I N G S Y S T E M A N D
S O L E N O I D S W I T C H
The voltage across the starter m otor and switch while
cranking the engine gives a good indication of any excessive
resistance.
N O TE: Engine m ust be at norm al operating
tem perature when test is made.
1. Inspect battery and cables to make certain that battery
has ample capacity for cranking and ignition.
2. Connect jum per wire to distributor term inal of coil
and to ground on engine, so that engine can be cranked
w ithout firing.
3. Connect voltm eter positive lead to the m otor terminal
on solenoid switch; connect voltmeter negative lead to ground
(Fig.6D-12s).
4. T urn ignition switch on, crank engine and take
voltm eter reading as quickly as possible. If cranking m otor
turns engine at norm al cranking speed with voltmeter reading
Fig. 6 D - 1 2 s -C ra n k in g V o lta g e T e s t C o n n e c tio n s
9 or more volts, the m otor and switch are satisfactory. If
cranking speed is below norm al and voltmeter reading is 9
volts or greater, the cranking m otor is defective.
CAUTION: D o n o t operate starter m o to r m ore
than 30 seconds at a tim e without pausing to allow
m otor to cool fo r at least two minutes; otherwise,
overheating a n d damage to m o to r m ay result.
5. If starter m otor turns engine at low rate of speed with
voltmeter reading less than 9 volts, test solenoid switch
contacts as follows:
6. W ith voltm eter switch turned to any scale above 12
volts, connect voltm eter negative lead to the m otor terminal
of solenoid switch, and connect positive lead to battery
terminal of switch (Fig. 6D-13s).
7. T urn ignition switch on and crank engine.
Immediately turn voltmeter switch to low scale and take
reading as quickly as possible, then turn switch back to higher
scale and stop engine.
The voltm eter will read not more than 2/1 0 volt if switch
contacts are satisfactory. If voltmeter reads more than 2/10
volt, switch should be repaired or replaced.