Starter Current Draw Test
A current draw test is performed after the battery has been checked and found to be fully charged and in good condition. The starting system should also be visually inspected for any physical defects or loose connections. Bring the engine to normal operating temperature before performing this test. This is because a cold engine requires more current than a warm engines does.
Use a VAT-40 or an appropriate clamp-on ammeter/voltage meter for slow start and no start troubleshooting. This test requires the specifications for the vehicle being tested.
1. Connect the tester leads to the correct positive and negative terminals and then connect the clamp-on amps pickup around one of the battery cables.
2. Set the voltage meter to Int 18V and adjust ammeter to read zero.
3. Disable the fuel or ignition so the engine will not start during test.
4. Crank the engine as you observe the testers ammeter and voltmeter.
5. Never crank engine for more than 15 seconds and allow the starter to cool for 2 minutes between cranks.
If you are using a separate ammeter and voltmeter instead of a VAT-40 the key is to observe the voltage and the amperage at the same time. The voltage should remain at or above specifications while cranking the engine. High current draw and low cranking speed indicate a faulty starter or possible engine problems. Low cranking speed and low current draw indicate excessive resistance in the starter circuit. Always check specifications and remember the bigger the engine the higher the current draw.
Slow cranking and high current draw typically indicate worn bearings or bushings inside the starter. Worn bushings will result in an off-center armature. This may result in poling and can throw off the alignment of the starters magnetic fields.