AUT 242 – Auto Electricity II Chapter 20 Cranking System Diagnosis and Service
OBJECTIVES After studying Chapter 20, the reader will 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. • Describe testing and repair procedures of the cranking circuit and components.
Bench testing Growler Shims Voltage drop KEY TERMS
STARTING SYSTEM TROUBLESHOOTINGPROCEDURE • OVERVIEW • 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.
STARTING SYSTEM TROUBLESHOOTINGPROCEDURE • STEPS INVOLVED • Following are the steps involved in the diagnosis of a fault in the cranking circuit. • STEP 1 Verify the customer concern. • STEP 2 Visually inspect the battery and battery connections. • STEP 3 Test battery condition. • STEP 4 Check the control circuit • STEP 5 Check voltage drop of the starter circuit
FIGURE 20–1 A theft deterrent indicator lamp of the dash. A flashing lamp usually indicates a fault in the system, and the engine may not start. STARTING SYSTEM TROUBLESHOOTINGPROCEDURE
Voltage Drop Is Resistance • Many technicians have asked, “Why measure voltage drop when the resistance can be easily measured using an ohmmeter?” Think of a battery cable with all the strands of the cable broken, except for one strand. If an ohmmeter were used to measure the resistance of the cable, the reading would be very low, probably less than 1 ohm. However, the cable is not capable of conducting the amount of current necessary to crank the engine. In less severe cases, several strands can be broken, thereby affecting the operation of the starter motor. Although the resistance of the battery cable will not indicate an increase, the restriction to current flow will cause heat and a drop of voltage available at the starter. Because resistance is not effective until current flows, measuring the voltage drop (differences in voltage between two points) is the most accurate method of determining the true resistance in a circuit.
Voltage Drop Is Resistance • How much is too much? According to Bosch Corporation, all electrical circuits should have a maximum of 3% loss of the circuit voltage to resistance. Therefore, in a 12 volt circuit, the maximum loss of voltage in cables and connections should be 0.36 volt (12 x 0.03 = 0.36 volt). The remaining 97% of the circuit voltage (11.64 volts) is available to operate the electrical device (load). Just remember: • Low-voltage drop = Low resistance • High-voltage drop = High resistance
VOLTAGE DROP TESTINGPURPOSE • Voltage drop is the drop in voltage that occurs when current is flowing through a resistance. • For example, a voltage drop is the difference between voltage at the source and voltage at the electrical device to which it is flowing. • The higher the voltage drop is, the greater the resistance in the circuit.
FIGURE 20–2 Voltmeter hookups for voltage drop testing of a solenoid-type cranking circuit. VOLTAGE DROP TESTINGTEST PROCEDURE
FIGURE 20–3 Voltmeter hookups for voltage drop testing of a Ford cranking circuit. VOLTAGE DROP TESTINGTEST PROCEDURE
FIGURE 20–4 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 0.20 volt (200 mV). VOLTAGE DROP TESTINGTEST PROCEDURE
VOLTAGE DROP TESTINGTEST PROCEDURE • STEP 1 Disable the ignition or fuel injection as follows: • Disconnect the primary (low-voltage) electrical connection(s) from the ignition module or ignition coils. • Remove the fuel-injection fuse or relay, or the electrical connection leading to all of the fuel injectors. • STEP 2 Connect one lead of the voltmeter to the starter motor battery terminal and the other end to the positive battery terminal. • STEP 3 Crank the engine and observe the reading while cranking. (Disregard the first higher reading.) The reading should be less than 0.20 volt (200 mV).
VOLTAGE DROP TESTINGTEST PROCEDURE • STEP 4 If accessible, test the voltage drop across the “B” and “M” terminals of the starter solenoid with the engine cranking. • STEP 5 Repeat the voltage drop on the ground side of the cranking circuit by connecting one voltmeter lead to the negative battery terminal and the other at the starter housing. Crank the engine and observe the voltmeter display. The voltage drop should be less than 0.2 volt (200 mV).
A Warm Cable Equals High Resistance • If a cable or connection is warm to the touch, there is electrical resistance in the cable or connection. The resistance changes electrical energy into heat energy. Therefore, if a voltmeter is not available, touch the battery cables and connections while cranking the engine. If any cable or connection is hot to the touch, it should be cleaned or replaced.
CONTROL CIRCUIT TESTINGPARTS INVOLVED • The control circuit for the starting circuit includes: • The battery • Ignition switch • Neutral or clutch safety switch • Theft deterrent system • Starter solenoid
FIGURE 20–5 A starter amperage tester uses an amp probe around the positive or negative battery cables. STARTER AMPERAGE TEST • REASON FOR A STARTER AMPERAGE TEST • TEST PREPARATION • SPECIFICTIONS
Watch the Dome Light • When diagnosing any starter-related problem, open the door of the vehicle and observe the brightness of the dome or interior light(s). The brightness of any electrical lamp is proportional to the voltage of the battery. Normal operation of the starter results in a slight dimming of the dome light. If the light remains bright, the problem is usually an • open in the control circuit. If the light goes out or almost goes out, there could be a problem with the following: • A shorted or grounded armature of field coils inside the starter • Loose or corroded battery connections or cables • Weak or discharged battery
STARTER REMOVALPROCEDURE • 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. • STEP 4 Disconnect and label 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.
FIGURE 20–6 The starter is located under the intake manifold on this Cadillac Northstar engine. STARTER REMOVALPROCEDURE
STARTER MOTOR SERVICE • PURPOSE • DISASSEMBLY PROCEDURE • STEP 1 Remove the starter solenoid assembly. • STEP 2 Mark the location of the through bolts on the field housing to help align them during reassembly. • STEP 3 Remove the drive-end housing and then the armature assembly. • INSPECTION AND TESTING
FIGURE 20–7 An exploded view of a typical solenoid-operated starter. STARTER MOTOR SERVICE
FIGURE 20–8 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). STARTER MOTOR SERVICE
FIGURE 20–9 Measuring an armature shaft for runout using a dial indicator and V-blocks. STARTER MOTOR SERVICE
FIGURE 20–10 Replacement starter brushes should be installed so the beveled edge matches the rotation of the commutator. STARTER MOTOR SERVICE
BENCH TESTING • Bench testing is the usual method and involves clamping the starter in a vise to prevent rotation during operation and connecting heavy-gauge jumper wires (minimum 4 gauge) to both a battery known to be good and the starter. • The starter motor should rotate as fast as specifications indicate and not draw more than the free-spinning amperage permitted. • 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 • 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 and tighten evenly. • STEP 5 Perform a starter amperage draw test and check for proper engine cranking.
FIGURE 20–11 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-TO-FLYWHEEL CLEARANCE • NEED FOR SHIMS • SYMPTOMS OF CLEARANCE PROBLEMS • PROCEDURE FOR PROPER CLEARANCE
Reuse Drive-End Housing to Be Sure • Most GM starter motors use a pad mount and attach to the engine with bolts through the drive-end (nose) housing. Many times when a starter is replaced on a GM vehicle, the starter makes noise because of improper starter pinion-to-engine flywheel ring gear clearance. Instead of spending a lot of time shimming the new starter, simply remove the drive-end housing from the original starter and install it on the replacement starter. Service the bushing in the driveend housing if needed. Because the original starter did not produce excessive gear engagement noise, the replacement starter will also be okay. Reuse any shims that were used with the original starter. This is preferable to removing and reinstalling the replacement starter several times until the proper clearance is determined.
SUMMARY • Proper operation and testing of the starter motor depends on the battery being at least 75% charged and the battery cables being of the correct size (gauge) and having no more than a 0.2 volt drop. • Voltage drop testing includes cranking the engine, measuring the drop in voltage from the battery to the starter, and measuring the drop in voltage from the negative terminal of the battery to the engine block. • The cranking circuit should be tested for proper amperage draw. • An open in the control circuit can prevent starter motor operation.
REVIEW QUESTIONS • What are the parts of the cranking circuit? • What are the steps taken to perform a voltage drop test of the cranking circuit? • What are the steps necessary to replace a starter?
CHAPTER QUIZ 1. A growler is used to test what starter component? • Field coils • Armatures • Commutator • Solenoid
CHAPTER QUIZ 2. Two technicians are discussing what could be the cause of slow cranking and excessive current draw. Technician A says that an engine mechanical fault could be the cause. Technician B says that the starter motor could be binding or defective. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 3. A V-6 is being checked for starter amperage draw. The initial surge current was about 210 amperes and about 160 amperes during cranking. Technician A says the starter is defective and should be replaced because the current flow exceeds 200 amperes. Technician B says this is normal current draw for a starter motor on a V-6 engine. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 4. What component or circuit can keep the engine from cranking? • Antitheft • Solenoid • Ignition switch • All of the above
CHAPTER QUIZ 5. Technician A says that a discharged battery (lower than normal battery voltage) can cause solenoid clicking. Technician B says that a discharged battery or dirty (corroded) battery cables can cause solenoid clicking. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 6. Slow cranking by the starter can be caused by all except ________ . • A low or discharged battery • Corroded or dirty battery cables • Engine mechanical problems • An open neutral safety switch
CHAPTER QUIZ 7. Bench testing of a starter should be done ________ . • After reassembling an old starter • Before installing a new starter • After removing the old starter • Both a and b
CHAPTER QUIZ 8. If the clearance between the starter pinion and the engine flywheel is too great, ________. • The starter will produce a high-pitched whine during cranking • The starter will produce a high-pitched whine after the engine starts • The starter drive will not rotate at all • The solenoid will not engage the starter drive unit
CHAPTER QUIZ 9. A technician connects one lead of a digital voltmeter to the positive (+) terminal of the battery and the other meter lead to the battery terminal (B) of the starter solenoid and then cranks the engine. During cranking, the voltmeter displays a reading of 878 mV. Technician A says that this reading indicates that the positive battery cable has too high resistance. Technician B says that this reading indicates that the starter is defective. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 10. A vehicle equipped with a V-8 engine does not crank fast enough to start. Technician A says the battery could be discharged or defective. Technician B says that the negative cable is loose at the battery. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B