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OBJECTIVES. After studying Chapter 19, the reader should be able to: Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “C” (Starting System Diagnosis and Repair). Explain how to disassemble and reassemble a starter motor and solenoid.
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OBJECTIVES After studying Chapter 19, the reader should be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “C” (Starting System Diagnosis and Repair). • Explain how to disassemble and reassemble a starter motor and solenoid. • Discuss how to perform a voltage drop test on the cranking circuit. • Describe how to perform cranking system repair procedures.
STARTING SYSTEM TROUBLESHOOTING • The proper operation of the starting system depends on a good battery, good cables and connections, and a good starter motor. • Because a starting problem can be caused by a defective component anywhere in the starting circuit, it is important to check for the proper operation of each part of the circuit to diagnose and repair the problem quickly.
VOLTAGE DROP TESTING • Voltage drop is the drop in voltage that occurs when current is flowing through a resistance. • Voltage drop testing of the wire involves connecting a voltmeter set to read DC volts to the suspected high-resistance cable ends and cranking the engine. FIGURE 19-1 To test the voltage drop of the battery cable connection, place one voltmeter lead on the battery terminal and the other voltmeter lead on the cable end and crank the engine. The voltmeter will read the difference in voltage between the two leads which should not exceed 0.2 volt (200 mV).
VOLTAGE DROP TESTING FIGURE 19-2 Voltmeter hookups for voltage drop testing of a GM-type cranking circuit.
VOLTAGE DROP TESTING FIGURE 19-3 Voltmeter hookups for voltage drop testing of Ford-type cranking circuit.
VOLTAGE DROP TESTING • If the difference in the two readings exceeds 0.5 volt, perform the following steps to determine the exact location of the voltage drop. • Connect the positive voltmeter test lead to the most-positive end of the cable being tested. The most-positive end of a cable is the end closest to the positive terminal of the battery.
VOLTAGE DROP TESTING • Connect the negative voltmeter test lead to the other end of the cable being tested. With no current flowing through the cable, the voltmeter should read zero because both ends of the cable have the same voltage. • Crank the engine. The voltmeter should read less than 0.2 volt. • Evaluate the results. If the voltmeter reads zero, the cable being tested has no resistance and is good. If the voltmeter reads higher than 0.2 volt, the cable has excessive resistance and should be replaced. However, before replacing the cable, make certain that the connections at both ends of the cable being tested are clean and tight.
CONTROL CIRCUIT TESTING • When the ignition switch is rotated to the start position, current flows through the ignition switch and neutral safety switch and activates the solenoid. FIGURE 19-4 A typical Ford solenoid on the left and a typical GM solenoid on the right.
CONTROL CIRCUIT TESTING • High current then flows directly from the battery through the solenoid and to the starter motor. • Therefore, an open or break anywhere in the control circuit will prevent the operation of the starter motor. FIGURE 19-5 GM solenoid ohmmeter check. The reading between 1 and 3 (S terminal and ground) should be 0.4 to 0.6 ohm (hold-in winding). The reading between 1 and 2 (S terminal and M terminal) should be 0.2 to 0.4 ohm (pull-in winding).
CONTROL CIRCUIT TESTING • If a starter is inoperative, first check for voltage at the S (start) terminal of the starter solenoid. • Some newer models with antitheft controls use a relay to open this control circuit to prevent starter operation.
CONTROL CIRCUIT TESTING FIGURE 19-6 Starter trouble diagnostic chart.
SPECIFICATIONS FOR A STARTER AMPERAGE TEST • A starter amperage test should be performed when the starter fails to operate normally (is slow in cranking) or as part of a routine electrical system inspection. FIGURE 19-7 Starter current can be measured by using a high current clamp and a digital multimeter or a specialized starting and charging tester.
SPECIFICATIONS FOR A STARTER AMPERAGE TEST • If exact specifications are not available, the following can be used as general maximum amperage draw specifications for testing a starter on the vehicle. 4-cylinder engines = 150 to 185 amperes 6-cylinder engines = 160 to 200 amperes 8-cylinder engines = 185 to 250 amperes
SPECIFICATIONS FOR A STARTER AMPERAGE TEST • Excessive current draw may indicate one or more of the following: 1. Binding of starter armature as a result of worn bushings 2. Oil too thick (viscosity too high) for weather conditions 3. Shorted or grounded starter windings or cables 4. Tight or seized engine 5. Shorted starter motor (usually caused by fault with the field coils or armature)
STARTER REMOVAL • After testing has confirmed that a starter motor may need to be replaced, most vehicle manufacturers recommend the following general steps and procedures. Step 1 Disconnect the negative battery cable. Step 2 Hoist the vehicle safely. Step 3 Remove the starter retaining bolts and lower the starter to gain access to the wire(s) connection(s) on the starter.
STARTER REMOVAL Step 4 Disconnect the wire(s) from the starter and remove the starter. Step 5 Inspect the flywheel (flexplate) for ring gear damage. Also check that the mounting holes are clean and the mounting flange is clean and smooth. Service as needed.
STARTER OVERHAUL • To remove the starter motor from the vehicle, first remove the negative battery cable from the battery to prevent any possible shorts from causing personal injury or property damage. • Before disconnecting the wiring, mark or tag the location of all wiring connections.
STARTER OVERHAUL FIGURE 19-8 Before disassembly of any starter, mark the location of the through bolts on the field housing. This makes reassembly easier. FIGURE 19-9 Removing the solenoid from the starter on a GM-type starter assembly.
STARTER OVERHAUL FIGURE 19-11 The brushes should be replaced if worn to less than 50% of their original length. Replace if less than 1/2 in.(13 mm) long. FIGURE 19-10 Rotate the solenoid to remove it from the starter housing. (Caution: The plunger return spring exerts a force on the solenoid and may cause personal injury if not carefully released.)
STARTER OVERHAUL FIGURE 19-12 An exploded view of a General Motors starter.
STARTER OVERHAUL FIGURE 19-13 To replace the starter drive unit, the retainer and clip must be removed from the armature shaft. A box-end wrench and a hammer can be used to pop the retainer off of the spring clip.
TESTING STARTER ARMATURES • After the starter drive has been removed from the armature, it can be checked for run out using a dial indicator and V-blocks FIGURE 19-14 Measuring an armature shaft for run-out using a dial indicator V-blocks.
GROWLER TEST FOR SHORTED ARMATURE WINDINGS • If an armature is shorted (copper-to-copper connection), it must be replaced or rewound by a specialist. FIGURE 19-15 Using a growler to check for shorted armature windings.
TESTING THE ARMATURE FOR GROUNDS • An open in an armature is usually observed visually as a loop that is broken or unsoldered where it connects to the commutator segments. • A loose or broken solder connection can often be repaired by resoldering the broken connection using rosin-core solder.
ARMATURE SERVICE • Some manufacturers recommend that the insulation between the segments of the armature (mica or hard plastic) be undercut. FIGURE 19-16 Replacement starter brushes should be installed so the beveled edge matches the rotation of commutator.
TESTING STARTER MOTOR FIELD COILS • With the armature removed from the starter motor, the field coils should be tested for opens and grounds using a powered test light or an ohmmeter. • The ohmmeter should indicate infinity (no continuity), and the test light should not light.
STARTER BRUSH INSPECTION • Starter brushes should be replaced if the brush length is less than one-half of its original length (less than 1/2 in. [13 mm]). • Many starters use brushes that are held in with screws and are easily replaced, whereas other starters may require soldering to remove and replace the brushes.
BENCH TESTING • Every starter should be tested before installation in a vehicle. • A typical amperage specification for a starter being tested on a bench (not installed in a vehicle) usually ranges from 60 to 100 amperes.
STARTER INSTALLATION • Following are the usual steps needed to be performed to install a starter. Step 1 Check service information for the exact wiring connections to the starter and/or solenoid. Step 2 Verify that all electrical connections on the starter motor and/or solenoid are correct for the vehicle and that they are in good condition. Step 3 Attach the power and control wires. Step 4 Install the starter, and torque all the fasteners to factory specifications.
STARTER DRIVE-TOFLYWHEEL CLEARANCE • Many starters use shims, which are thin metal strips between the flywheel and the engine block mounting pad to provide the proper clearance. FIGURE 19-17 A shim (or half shim) may be needed to provide the proper clearance between the flywheel teeth of the engine and the pinion teeth of the starter.
STARTER DRIVE-TOFLYWHEEL CLEARANCE • To be sure that the starter is shimmed correctly, use the following procedure. Step 1 Place the starter in position and finger tighten the mounting bolts. Step 2 Use a 1/8 in. diameter drill bit (or gauge tool) and insert between the armature shaft and a tooth of the engine flywheel.
STARTER DRIVE-TO FLYWHEEL CLEARANCE Step 3 If the gauge tool cannot be inserted, use a full length shim across both mounting holes which will move the starter away from the flywheel. Step 4 Remove a shim(s) if the gauge tool is loose between the shaft and the tooth of the engine flywheel. Step 5 If no shims have been used and the fit of the gauge tool is too loose, add a half shim to the outside pad only. This moves the starter closer to the teeth of the engine flywheel.
STARTING SYSTEM SYMPTOM GUIDE • The following list will assist technicians in troubleshooting starting systems.
LIGHTS ON TO CRANK • This simple theft deterrent uses a relay to prevent the engine from cranking unless the parking lights are turned on first. FIGURE 19-18 This simple theft deterrent circuit will prevent the engine from cranking unless the lights are turned on first. The lights do not have to remain on after the engine starts.
