Chapter A: General Diagnosis
28
Circuit Resistance Tests
If the current draw and cranking voltage tests indicate
that the problem lies in one of the starting system elec-
trical circuits, perform circuit resistance tests to pinpoint
the problem.
These tests locate the point of high resistance in the cir-
cuit that is causing excessive voltage drop. The resis-
tance usually occurs at one of the connections in the cir-
cuits, but internally defective wires and cables may also
be at fault. As a general rule, acceptable voltage drop
standard in starting systems is a maximum of 0.1 volt
per connection. A greater voltage drop causes starter
motor performance problems.
The starting system has three circuits:
•Insulated
•Ground
•Control
The insulated circuit carries the high current needed to
operate the starter motor, the ground circuit provides a
return path to the battery for power supplied by the in-
sulated circuit, and the control circuit includes all the low
current wiring and devices used to open and close the
insulated circuit. To locate the source of high resistance,
perform voltage drop tests recommended by the man-
ufacturer. Take readings while the starter motor is crank-
ing, or use a carbon pile to load the circuit, figure 1-34.
Momentarily load the circuit to approximately 150 to 200
amps, and switch the load off quickly to prevent drain-
ing the battery. Test the starter ground circuit in a simi-
lar manner, figure 1-35. Perform voltage drop tests on
the control circuit as needed.
If any of the tests indicate an internal problem, the
starter motor must be removed from the vehicle and ei-
ther repaired or replaced.
Starter Removal
The following is a typical starter motor removal se-
quence. Always consult the repair manual for the vehi-
cle being serviced. To remove the starter:
1. Disconnect the negative battery cable.
2. Raise the vehicle on safety stands or a hoist high
enough to access the starter motor.
3. Disconnect any suspension components that are
likely to interfere with removing the starter from the
chassis.
4. Loosen or remove exhaust pipes and other com-
ponents that interfere with starter motor removal.
5. Disconnect and label all wires and cables to the
starter motor or solenoid.
6. Remove any heat shields and brackets covering the
starter motor.
7. Remove any mounting bolts and shims securing
the starter motor to the engine.
8. Slide the starter free of the bellhousing and guide it
out of the chassis.
Starter Installation
When replacing a starter motor, make sure the new unit
meets the requirements of the vehicle. Some vehicles
require a high-temperature starter with an extra field
coil, brush lead and solenoid winding insulation as well
as a high-temperature solenoid cap. To install a starter
motor:
VHz~
~
10A
RPM
+
COM
A
C F
RPM
V
%
OFF
VHz
IGNITION
SWITCH
NEUTRAL
SAFETY
SWITCH
VOLTMETER
REMOTE
STARTER
SWITCH
BATTERY
+
-
STARTER
STARTER
RELAY
Fig. 1-33
Typical voltmeter connections for performing a starter
motor cranking voltage test.
VHz~
~
10A
RPM
+
COM
A
CF
RPM
V
%
OFF
VHz
AMPS
30
0
20
40
50
OFF
SOLENOID
STARTER
MOTOR
IGNITION
SWITCH
CHASSIS/
BODY
ENGINE
A
BATTERY TESTER
+
-
Fig. 1-34.
Connections for loading the system and testing for voltage
drop on the insulated side of the starting system.
Summary of Contents for ASE-A8
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