How to test spark plug?

How to test spark plug?


Testing spark plugs is an essential part of regular vehicle maintenance. Spark plugs play a crucial role in the ignition process, and ensuring they are in good working condition is vital for optimal engine performance. In this article, we will explore the various methods and steps involved in testing spark plugs to identify any issues and determine if they need to be replaced.

Visual Inspection

Materials used: Flashlight, gloves

The first step in testing spark plugs is a visual inspection. Start by removing the spark plug wires one at a time, taking care not to mix them up. Use a flashlight to inspect the spark plugs for any signs of damage, such as cracks, carbon deposits, or oil fouling. If you notice any of these issues, it is an indication that the spark plug needs to be replaced.

Resistance Testing

Materials used: Digital multimeter

Resistance testing is another method to check the condition of spark plugs. Begin by setting the digital multimeter to the resistance or ohms setting. Then, connect the multimeter’s leads to the metal terminal and the threaded part of the spark plug. The resistance reading should fall within the range specified by the manufacturer. If the reading is significantly higher or lower, it indicates a faulty spark plug that needs to be replaced.

Spark Testing

Materials used: Spark plug tester

Spark testing is an effective way to determine if a spark plug is generating a spark. To perform this test, connect the spark plug tester to the spark plug wire. Ground the tester by attaching it to a metal part of the engine. Start the engine and observe the tester for a strong, blue spark. If there is no spark or the spark is weak, it indicates a faulty spark plug that should be replaced.

Compression Testing

Materials used: Compression tester

Compression testing can help identify issues with the spark plug, as well as other engine components. Start by removing all the spark plugs from the engine. Then, connect the compression tester to the spark plug hole of the first cylinder. Crank the engine a few times and observe the pressure reading on the tester. Repeat this process for each cylinder. If there is a significant difference in compression between cylinders, it may indicate a faulty spark plug or other engine problems.


Regularly testing spark plugs is crucial for maintaining optimal engine performance. Visual inspection, resistance testing, spark testing, and compression testing are effective methods to identify any issues with spark plugs. By following these steps, you can ensure that your spark plugs are in good working condition and replace them if necessary, thereby improving the overall performance and efficiency of your vehicle.