Unit 4 Starting System Circuit Operation and Testing

Unit 4 Starting System Circuit Operation and Testing

Introduction • Almost every system relies on: – Electrical and electronic components – Electronic control modules – Networking systems • Automobiles have: – 12 -volt storage battery – Engine starting system – Electrical charging system

Engine Starting Systems— Starter Draw Testing (1 of 3) • Testing is a good indicator of overall starter motor performance. – Perform tests with fully charged and correct capacity battery. – Can be tested in two ways • On vehicle—starter draw test • Off vehicle—no-load test

Engine Starting Systems— Starter Draw Testing (2 of 3) • Test current draw under load. – Easier while motor mounted in the vehicle – Draw highest when starter pinion gear first engages with flywheel – As starter motor and engine cranking speed increase, current draw decreases and stabilizes.

Engine Starting Systems— Starter Draw Testing (3 of 3) • Variety of equipment used, but should have: – Inductive high-current ammeter—measure cranking current flow – Voltmeter—measure cranking voltage • Disabled engine should crank but not start. • Measure current flow, voltage during cranking.

Engine Starting Systems—Testing Starter Circuit Voltage Drop (1 of 5) • Electrical circuit – High-current circuit • Battery • Main battery cables • Solenoid contacts • Heavy ground cables • Control circuit – Activates solenoid – Either PCM controlled or non-PCM controlled

Engine Starting Systems—Testing Starter Circuit Voltage Drop (2 of 5) • High-current circuit susceptible because of larger amount of current – Starter must be activated by the solenoid. – Starter must click when ignition is engaged. – If no click, test control side of starter circuit.

Engine Starting Systems—Testing Starter Circuit Voltage Drop (3 of 5) • Use voltmeter or DVOM to measure drop on all circuit parts. – Voltmeter with minimum/maximum range is useful. • Records and holds maximum voltage drop for particular operation cycle – Keep circuits under load.

Engine Starting Systems—Testing Starter Circuit Voltage Drop (4 of 5) • DVOM connected in parallel across component or circuit part being tested – Test large sections first, then individual components to locate drop. – Check specifications, but usually no more than 0. 5 volts for a 12 -volt circuit.

Engine Starting Systems—Testing Starter Circuit Voltage Drop (5 of 5) • Perform same test on positive side of circuit. – Starter cable connected to input of solenoid – Output connected to input of starter motor – Measure drop from positive battery post to starter motor input. • Disable engine.

Engine Starting Systems— Inspecting/Testing the Starter Control Circuit (1 of 4) • Made up of: – – – Battery Fusible link Ignition switch Neutral safety switch Clutch switch starter relay Solenoid windings

Engine Starting Systems— Inspecting/Testing the Starter Control Circuit (2 of 4) • If controlled by PCM, understand all circuits. • Before performing tests, confirm customer’s issues. – Consult manufacturer diagrams for circuit operation. – Identify all components.

Engine Starting Systems— Inspecting/Testing the Starter Control Circuit (3 of 4) • First test with DVOM. – – Place red lead on starter input terminal. Place black lead on starter housing. Measure voltage with key in crank position. Faulty if less than 10. 5 volts at control circuit

Engine Starting Systems— Inspecting/Testing the Starter Control Circuit (4 of 4) • If faulty, voltage drop test on power side: – If less than 0. 5, measure starter ground circuit. – If excessive, do individual voltage drops on ground leg. – If both within specs, measure resistance of solenoid pull-in and hold-in windings.

Engine Starting Systems— Inspecting/Testing Relays, Solenoids (1 of 5) • Before any tests: – Ensure battery is charged and in good condition. – Check wiring diagrams to determine: • Circuit operation • Identification • Location of all components

Engine Starting Systems— Inspecting/Testing Relays, Solenoids (2 of 5) • Test 1—measure relay winding resistance – If out of specs, needs replacement • Relay okay, test contacts for voltage drop. – Use adapter between the relay and relay socket. • Lab test—on relays with suppression diode in parallel with a relay winding

Engine Starting Systems— Inspecting/Testing Relays, Solenoids (3 of 5) • Solenoids difficult to test, with poor access – Limited to voltage and voltage drop tests on main contacts – For other tests, starter motor may need to be removed; for example: • Pull-in test • Hold-in winding test

Engine Starting Systems— Inspecting/Testing Relays, Solenoids (4 of 5) • Voltage drop test across solenoid contacts – Place red lead on solenoid B-positive input. – Place black lead on solenoid B-positive output. – Voltage drop should be less than 0. 5 volts. • If not, replace starter assembly.

Engine Starting Systems— Inspecting/Testing Relays, Solenoids (5 of 5) • Solenoid winding testing—must partially disassemble solenoid – Disconnect control circuit connector from solenoid. – If solenoid and starter operate, likely a fault in the control circuit – If solenoid or starter does not work, starter faulty

Engine Starting Systems—Removing and Installing a Starter • Usually located close to flywheel end of engine – May need to remove components or covers for access – Often more easily reached from under the vehicle • Always disconnect negative battery lead first.

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (1 of 7) • Slow cranking: – Example, electrical fault: High resistance in solenoid contacts • Replace starter. – Example, mechanical engine fault: Spin main bearing causing drag on crankshaft • Rebuild entire engine.

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (2 of 7) • Typical electrical problems: – – Loose, dirty, or corroded terminals and connectors Discharged or faulty battery Faulty starter motor Faulty control circuits

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (3 of 7) • Typical mechanical problems: – – Seized pistons or bearings Hydrostatic lock from liquid in cylinders Incorrect ignition or valve timing Seized alternator or other belt-driven device

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (4 of 7) • Determine tests by the likelihood of the fault. – Example: If vehicle in a parking lot, better chance fault is electrical • Ease of conducting test/visual – Example: Easier to perform starter draw test than inspect main bearings

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (5 of 7) • Measure starter motor current draw first. – Slow crank with low draw—high resistance in main starter circuit or the starter – Slow crank with high draw—fault in the starter or engine mechanical fault

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (6 of 7) • If mechanical: – Check oil and coolant for contamination. – If coolant and oil mixed, check head gasket or cracked head/block. • If no contamination, turn engine over to check if it is tight.

Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (7 of 7) • If hard to turn, remove accessory drive belt and spin each accessory before trying to turn engine over again. • If still hard to turn over: – Disassemble components to check them individually.

Summary • Testing starter motor current draw is a good indicator of overall starter motor performance. • Amperage draw can help to differentiate mechanical from electrical failure. • Voltage drop is key test for isolating electrical faults.

Credits • Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.