Multimeters in Automotive Repair
Testing Ignition Coils
Fluke analogue/digital multimeters can test resistance from 0.01Ω (Type 88) to 32MΩ. This makes testing ignition coils very accurate and easy. Typical multimeters cannot test resistances below 1Ω.
Measuring internal coil resistance
If you suspect that the ignition coil is not working properly you should check the resistance of the primary and secondary coils. The tests should be carried out with the car warm and cool and each connector should be tested. The primary resistance of the coil is very low while the secondary resistance is high. The manufacturer's specifications should be consulted. Empirical values are 0 - a few Ω for the primary and 10 KΩ or a little more for the secondary.
Testing the spark plug connection
Spark plugs that have been in use for many years and that show signs of a possible spark plug problem should be checked. Not all connections have the date the spark plug was manufactured on them. High heat can cause the spark plug base to stick to the spark plug. So removing the spark plug may damage the precision brittle wires in the insulated wires. So when removing it, rotate it a few times repeatedly first. If you suspect a problem, you should test the resistance of the connecting wire while slowly twisting and rotating it. The resistance value is about 30 kΩ per metre. The size of the value is related to the type of wire. Some will be much smaller. For the purpose of measurement it is best to make a comparison with the wires of other spark plugs of the engine.
Capacitance
A Fluke analogue/digital multimeter can also test the capacitance of a car, a change in the die helium pointer tells the multimeter that it is charging the capacitor. You can find the resistance varying from 0 to infinity, make sure the capacitance should be tested from both directions and also test the capacitance in hot and cold conditions.
Testing the leakage of capacitors
Test the leakage of the capacitor using the multimeter's resistance setting. The resistance should grow to infinity when the capacitor is charging. And any other value indicates that the capacitor should be replaced. Test the capacitor by disconnecting it from the car circuit.
Hall-Effect Position Sensors
Hall-effect sensors have replaced many of the ignition points on a switchboard and are used to directly detect the position of the crankshaft and cams in non-switchboard ignition systems, which tells the computer when to fire the coils. A Hall effect sensor produces a voltage proportional to the strength of the magnetic field passing through it. It can come from a magnet or an electric current.
