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Diagnose the Starting System

This guide provides essential steps for diagnosing starter system problems in vehicles. Begin by ensuring a strong battery to test the starter effectively. Measure cranking voltage, RPM, and amps while disabling the fuel system to facilitate accurate diagnosis. Understand that slow cranking can indicate starter and battery issues, with specified maximum cranking amps varying by engine type. Investigate volt drop in starter cables, which can lead to performance failures. Intermittent starting issues may arise from defects in the starter control circuit. Learn the best practices for effective troubleshooting.

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Diagnose the Starting System

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  1. Diagnose the Starting System

  2. Fender Covers !

  3. You must have a strong battery to test the starter

  4. Test the Starter Circuit • Cranking Voltage • Cranking R. P. M. • Cranking Amps

  5. Move Amp Probeto measure all amps leaving battery

  6. Disable Fuel System

  7. Turning off the fuel allows starter to crank long enough for an accurate diagnosis

  8. If it is easy….…use a remote starter

  9. Record cranking Voltsand cranking Amps

  10. Starter amp draw will be high until the starter motor reaches maximum RPM • Cranking longer than 10 or 15 seconds will overheat the starter • Starter motors that crank slowly lead to starter and battery problems

  11. Listen for slow cranking

  12. Cranking voltage MUST stay above 10 volts • Maximum Cranking Amps 4 cylinder = 150 Amp 6 cylinder = 200 Amp 8 cylinder = 250 Amp • These are ONLY approximate specificationsand not valid on diesel engines.

  13. Slow turning starters cause trouble • Engines will be harder to start requiring longer cranking times • Starters will tend to overheat • Batteries will wear out sooner • By carefully listening to many different engines, you will learn to identify slow cranking R.P.M.’s

  14. Volt Drop Starter Cables • Resistance in the high amp starter (battery) cables will cause slow cranking • Replacing a starter motor without checking volt drop may cause the new starter to fail • High amp starter cables should have less than ½ volt drop.

  15. Volt drop negative cable(s) starter motor housing negative battery terminal

  16. Crank starter to read volt drop

  17. Volt drop positive cable(s)

  18. Hook to high amp cable

  19. Diagnose Intermittent or No Crank • Intermittent, or no starter motor operation may be caused by a defect in the starter control circuit • Begin by understanding the system

  20. This system has 2 starter control circuits.

  21. Set-up for #1 control circuit.

  22. Set-up for positive side of #2 control circuit.

  23. Set-up for ground side of #2 control circuit.

  24. Defects in control circuit #1, or control circuit #2, will cause intermittentor No Start

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