How To Test a Spark Plug With a Multimeter

Spark plugs, the seemingly small parts of your car, are often underappreciated by car owners. These tiny parts are so important for your car engine that without a spark plug, an engine wouldn’t run at all. With the passage of time and the usage of the engine, you may often get a bad spark plug. Imagine going for a trip, loading all your luggage in the car, and the car won’t start. This may happen because of a faulty spark plug.

Therefore, it is essential that you always check your spark plugs and see if they are functional or not. This can be done by regular testing, and the best device for testing a spark plug is a multimeter. In this article, we will see how to test a spark plug with a multimeter. In order to understand the values that the multimeter shows, we need to understand the working of a spark plug and the problem that may have arisen.

The Working of A Spark Plug:

A spark plug ignites fuel and air mixture and measures the ionization in the engine cylinders. It does this with the help of electrodes. Before ignition, there is no flow of current between the two electrodes. This is because the air acts as an insulator. When you ignite it, a high voltage is produced between the two electrodes, the gases ionize, and they become a conductor. Then, the current passes, and the engine starts.

If there is a problem with your spark plug, you may find it difficult to start the engine. However, in order to check whether the spark plug is working or not, a multimeter is used. It is a device used to measure voltage, resistance, current, and other values.

There are two types of multimeters; analog multimeters and digital multimeters. Both of these can be used to test the working of a spark plug. You need to read the current, resistance, and voltage in the circuit of the spark plug, all of which are explained below.

Testing Your Spark Plug With an Analog Multimeter:

First, let’s look at how to test a spark plug with an analog multimeter.

Measuring the Voltage:

The steps you need to follow in order to measure the voltage of your spark plug with an analog multimeter are as follows.

  1. Identify the probes on your spark plugs, and insert them into the multimeter probes.
  2. To efficiently measure the voltage of your spark plug circuit, you need to make sure that you accommodate the highest value. To do this, set your analog multimeter range properly. You may get case damage due to the high voltage, so be careful with that.
  3. Probe the low voltage and then the high voltage.
  4. Now, you will see a positive deflection. Change the range accordingly until you have the largest deflection on the multimeter.
  5. Record the reading.
  6. Always remember to return the analog multimeter to its highest voltage value in order to avoid any case damage to the device.

Measuring the Current:

Measuring the current in the circuit of your spark plug is different from other measurements. Because the electrons flow around a circuit, circuit-breaking is important while measuring the value. Remember to lower the resistance of the spark plug to make sure that it does not affect the operations of the circuit.

Now, let’s see how to measure the current of your spark plug’s circuit using an analog multimeter.

  1. Insert the probes of the spark plug into the multimeter probes.
  2. Set the switch to the type of current measurement you need.
  3. Select the highest range of the current measurement value.
  4. Adjust the value of the multimeter so that maximum deflection is attained. This is done to make sure that the reading is accurate.
  5. Record your readings.

Measuring the Resistance:

Before you take any measurements of the resistance in the circuit, make sure that you set the analog multimeter to zero. Then, follow the steps mentioned below.

  1. Identify the probes of the spark plug and insert them correctly into the sockets of the multimeter.
  2. Select the maximum range. Again, this is done to make sure that you get an accurate reading.
  3. Form a short circuit by placing the two probes together.
  4. Adjust the range of the multimeter to zero.
  5. Check your reading and note it down.
  6. Turn the device off.

Now that we know how to test a spark plug with an analog multimeter let’s look at the same process done through a digital multimeter.

Testing a Spark Plug With a Digital Multimeter:

The following methods are used to measure the current, voltage, and resistance of the spark plug.

Measuring the Voltage:

  1. Identify the electrodes of the spark plug and connect them to the probes of the multimeter.
  2. Turn on the device.
  3. Set the largest value of the range mentioned on the device.
  4. Probe the low voltage first, then the high voltage.
  5. Make adjustments accordingly to the range switch.
  6. Note the readings.
  7. Remove the probes and turn the multimeter off.

Measuring the Current:

  1. Identify the probes, connect them to the multimeter and turn it on.
  2. Set the measurement type of the device to current.
  3. Select the maximum range of the current value on the device to prevent overloading the multimeter.
  4. Optimize the device accordingly.
  5. Record the readings.
  6. Set the range back to maximum voltage and turn the device off.

Measuring the Resistance:

  1. Identify the probes of the spark plug and connect them to the multimeter.
  2. Turn the multimeter on.
  3. Select the range of the resistance value.
  4. Record the readings.
  5. Turn the device off.

Wrapping it up:

Regular testing of your spark plugs can prove to be beneficial for the engine of your car, and it prolongs their life by ensuring maximum usage. With the help of the methods mentioned above, you can easily test your spark plug using a multimeter, either analog or digital.  

Also, learn how to:

Flush an Automotive AC System

Test a 3-Wire Crank System

Daniel Wood

Daniel, who is a mechanical engineer and hobbyist mechanic by profession has been specializing in electronic equipment for the past four years. He worked as an engineer at one of these manufacturing plants that specializes exclusively on this type equipment before opening up his own shop where he does research into different machines all day long!