Starting System Circuit Operation and Testing Unit 4 Starting System Circuit Operation and Testing

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

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 Control circuit High-current circuit Activates solenoid Battery Either PCM controlled or non-PCM controlled Main battery cables Solenoid contacts Heavy ground cables

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.

Typical electrical problems: 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

Typical mechanical problems: 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

Determine tests by the likelihood of the fault. 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

Measure starter motor current draw first. 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

If no contamination, turn engine over to check if it is tight. 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.

If still hard to turn over: 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.

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