GMC 4000 Series Service Manual page 409

Sec. 6Y
Page 398
STARTING SYSTEM
Figure 3 — Starter D isengagem ent and
Lock-Out (EG $500— 6500)
r e la y op eratin g c o il to b reak c ir c u it to sta r te r
solenoid, thus disengaging the starter if engine
control switch is not released after engine is start­
ed. This also prevents starter from being accident­
ally engaged by placing engine control switch in
"START" position while engine is running.
STARTING CIRCUIT TESTS
(ON VEHICLE)
Although the starter cannot be checked against
specifications on the vehicle, checks can be made
for excessive resistance in the starter circuit.
CAUTION: To make these checks on
gasoline engine models, disconnect the
primary lead at the distributor to prevent
engine starting. On Diesel models, pull
stop knob on instrument panel out to set
the injection pump in "N O -F U E L " (Stop)
position to prevent engine starting.
Figure 4 — Starter D isengagem ent and
Lock-Out (D L A /D L V 4000)
G M C S E R V I C E M A N U A L
ing engine during each check, measure resistance
in various parts of the circuit as follows:
checks, do not operate starting motor continuously
for more than 30 seconds to avoid overheating;
V -l - Check V -l with voltmeter leads connected
V-2 - Check V-2 with voltmeter leads connected
V-3 - Check V-3 with voltmeter leads connected
checks exceeds 0.2 volts, excessive resistance is
indicated in that part of the circuit being checked.
Locate and eliminate the cause of excessive volt­
age drop in these circuits in order to obtain max­
imum efficiency from the starting system . Cause
of excessive resistance may be loose, corroded,
or dirty connections, or frayed cables.
sure battery is not discharged, then check solenoid
operation. If the solenoid fails to operate, the
trouble may be due to excessive resistance in the
starter control circuit. Check all wiring and con­
nections from ignition or control switch to solenoid
for loose or corroded connections. If cause of ex­
cessiv e resistance is not apparent, connect a short
jumper lead across the solenoid battery and switch
term inals. If solenoid operates with jumper lead
connected, trouble is in the control circuit. Check
for defective ignition or control switch. If solenoid
does not operate with jumper lead connected, so le­
noid is defective and must be replaced.
Figure 5 — Voltmeter Connections for
Checking Circuits (Typical)
R efer rin g to fig u r e 5 and w ith sta r te r crank ­
IMPORTANT: When performing the following
from battery positive post to battery term ­
inal on the starter solenoid.
from solenoid battery terminal to solenoid
motor terminal.
from battery negative post to starter field
frame.
If voltmeter reading in any of the previous
If starter fails to crank engine, first make