How to Test a Spark Plug Using a Multimeter

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Imagine you are planning to go for a trip, and after loading your luggage in your car, the engine fails to start. This could be due to bad spark plugs. Therefore, it is essential to ensure that the spark plugs in your engine are well functional. You can do this by regularly testing them. The best testing device is a multimeter. This article explains how you can test a spark plug using a multimeter.

A spark plug is a device fitted in the head of a cylinder of a combustion engine to ignite compressed fuel and air using an electric spark. It exchanges heat by removing thermal energy that is unwanted from the combustion chamber and transfers heat to the cooling system of the engine.

The main functions of a spark plug are to ignite fuel and air mixture and to measure the ionization in the engine cylinders.

Operations of a spark plug

A spark plug has two electrodes. Before igniting, there is usually no flow of current because of the air and fuel in the gap, which acts as an insulator. An ignition coil generates a high voltage that connects to the spark plug, and the voltage develops between the two electrodes.

As the voltage increases, the gases undergo an ionization process. Once the gases are ionized, they become a conductor, and the current begins to flow. The voltage required for spark plugs to ‘fire’ is high, above 25,000 volts.

If your plug is not working, you could experience difficulties with your engine. However, to verify if your spark plug is working, you can use a multimeter. A multimeter is an electronic device used for measuring resistance, voltage, current, and other values.

There are two types of multimeters:

1. Analog multimeter

As the name depicts, it uses analog techniques to display measurement readings. It is a type of multimeter that has a graduated scale and a needle that moves over it. They are mainly used to detect slow voltage changes. They have high sensitivity and low resistance, and this makes it exceptional.

2. Digital multimeters

This is an electronic multimeter that displays readings on a screen. They are the most preferred multimeters due to their high accuracy, high digital resistance, and are easy to read.

Having understood what a spark plug is and how it works, lets now look at how you can test it using a multimeter. From the definition, a multimeter measures current, resistance, and voltage. To verify that your spark plug is working well, you need to measure the current, voltage, and resistance in its circuit. You can either use an analog multimeter or a digital multimeter.

Measuring voltage using an analog multimeter

These are the steps you need to follow to measure current in your spark plug:

  1. Analog multimeters have different sockets for voltage. Inset the spark plug probes into the multimeter probes.
  2. To make sure you accommodate the highest value, set the multimeter range well, and have a little allowance in case damage resulted due to high voltage.
  3. Probe the point with low voltage first, and then probe the point with high voltage.
  4. Once you obtain a positive deflection, make adjustments to your range, until you see the largest deflection.
  5. Do the reading and record it.
  6. It is advisable always to return the multimeter to its highest voltage range to avoid damage to the device.

Measuring voltage using a digital multimeter

  1. Connect the spark plug electrodes to the multimeter probes appropriately.
  2. Turn on the device
  3. Set the range of the device to have the largest value prospected.
  4. Probe the point with low voltage first.
  5. Probe the point with higher voltage.
  6. To obtain the best reading, make some adjustments to the range switch.
  7. Do the reading and note it.
  8. Remove the probes and turn off the multimeter.

Measuring current in a spark plug using a multimeter

The current measurement is slightly different from other measurements. This is because current entails electrons flow around a circuit. When measuring current, circuit breaking is necessary. Then insert the multimeter so that the current can pass through it. Lowering the resistance of the spark plug is necessary so that the multimeter does not interfere with the circuit’s operations.

Using an analog multimeter
  1. Correctly insert the spark plug probes into the multimeter.
  2. Set the switch to the current measurement type and select the highest range.
  3. Adjust the multimeter to gain the maximum deflection, to have a more accurate reading.
  4. Record your reading.
Using a digital multimeter
  1. Connect the probes of the spark plug with the device correctly and turn on the multimeter.
  2. Set the device range measurement type as current and select the maximum range. This prevents overloading in the multimeter.
  3. ​To obtain the best reading, optimize your device.
  4. Record your reading.
  5. To avoid damage, set the range back to maximum voltage.

Measuring resistance in a spark plug using a multimeter

Measuring the resistance is important as it affects the flow of current. If the resistance is low, the current flow will be high, and if the resistance is high, the correspondence is a low flow of current. You can use either a digital multimeter or an analog multimeter to measure the resistance.

Using an analog multimeter

Before making any measurement using an analog multimeter, you need to ‘zero’ the meter. To take the measurement:

  1. Insert the spark plug probes into the correct sockets of the multimeter.
  2. Select the maximum range to get an accurate reading.
  3. Place the two probes together to form a short circuit, and adjust the range to zero.
  4. Check your reading and note it, and turn-off the device.
Using a digital multimeter

When using this multimeter, it is not necessary to zero the meter, since it produces a direct reading. Below are the steps you need to follow.

  1. Connect the plug probes to the multimeter correctly.
  2. Turn on the multimeter.
  3. Select a range close to the prospected value.
  4. Take the reading, record it, and turn off the device.

To Wrap up

In conclusion, ensuring the spark plugs of your engine are working well is important. Regular testing of the plugs is one way you can ensure they are in good condition. The best thing is that you can do it yourself if you follow the steps explained in the article.

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