Starter Motor Testing

Starter Motor on car testing

Before we do the actual assesment, we get the opportunity to practice on some of the cars in the workbay.

Make of vehicle: Mazda                       Model: 323
Year of manufacture: 1998

Is the vehicle equipped with an Automatic transmission?          No
Is the vehicle equipped with any device that requires a power source for its memory?       Yes
 
What would you do before you disconnect the battery to ensure no memory loss? 
You would connect a back up 9v battery in the cigarette lighter and then disconnect the battery.

Before we start any testing on the vehicle, we must de - activate the ignition or fuel injection system, so as not to get a shock or have fuel spraying out of the injectors whilst we are conducting testing. We must check the battery for serviceability. After we have selected the correct range on the multi meter and then put the transmission in neutral if it is an automatic, we can then carry out testing.

Check the OCV of the battery:             12.6v
Percentage of charge:                            100%

To check the OCV of the battery we place our positive tester onto the positive terminal of the battery, and place the negative tester onto the negative terminal of the battery, the OCV or 'Open Circuit Voltage' reading will be displayed on the multimeter.

Check the available voltage across the battery terminal whilst cranking the engine:
Cranking voltage specification:             9.5v
Cranking voltage:                                  10.31v

This test is done the same as the OCV test, except that the engine is being cranked while this test is taking place. On this occasion, this battery passed, if it were to fail, it would have to be retested to determine its condition and whether it needs to be replaced.

Next we had to check the starter curcuit for voltage drop.

Check the loss between battery positive post and solenoid starter input stud whilst cranking:
Specification - less that 0.20v              Volts Drop - 0.2v1                       PASS

Check loss across solenoid main input and output terminal studs whilst cranking:
Specification - less than 0.10v              Volts Drop - 0.00v2                    PASS

Check loss between battery negative and starter motor body whist cranking:
Specification - less than 0.20v              Volts Drop - 0.29v3                    FAIL

Maximum voltage drop is:
Maximum allowed - 0.50v                     Total Volts Drop - 0.31v            PASS

Checking the starter motor current draw

Starter current draw specification: 125- 175 amps.

To check the starter motor current draw amps, we had to use a clamp ammeter set to 400 amps DC. We had to zero the meter to gain an acurate reading. Once it was ready for use we had to place the ammeter around the positive battery lead anywhere between the positive terminal and the "B" terminal of the solenoid whilst someone was cranking the engine, pressing hold when the reading came on screen so as not to gain the wrong reading later on.

Starter current draw:              135 amps                       PASS


After this test was completed, we then had to wait for our assesment on the following day, to show what we had learned.