How to Test Your Spark Plugs

Engine misfires are fairly common among older or ill-maintained engines; but even fairly new cars fail to start if their spark plugs don’t produce the “spark” required to start an engine. Like any engine component, spark plugs can wear out over time. Spark plugs make sure that combustion is provided in the engine while all the while making sure that power is supplied to your engine from the battery. But with hundreds of engine components to look out for, it might be difficult to diagnose the problem with your car.

Spark plugs can be particularly difficult to assess without knowing what to look for. A worn out spark plug can lead to anything from rough car idling to engine cylinder misfires. But by testing your spark plugs regularly, you’ll be able to ward off problems with your engine long before they become a serious problem.

Check for Symptoms of a Bad Spark Plug

You can easily check if your spark plugs are the cause of your engine trouble by keeping an eye out for a number of symptoms. If you notice a substantial decrease in fuel mileage, erratic car idling, frequent cylinder misfires or regular radio interference, your spark plugs could need replacing. Since spark plugs are electrical in nature, bear in mind that they could have a profound effect on the electronics of your car.

Disconnect the Spark Plug

If you feel that a spark plug is a cause of concern, or if you simply want to verify its condition, disconnect the spark plug. Make sure to use a spark plug wrench to safely remove the spark plug without the risk of electrocution. To properly diagnose the effect of the spark plug on your engine, make the disconnection while the engine is running and do so one spark plug at a time.

Check the Effect on the Engine

After disconnecting one spark plug, check if there is a significant change to your engine performance. If your engine drops in speed or begins to hum erratically after the disconnection, this is a clear sign that the spark plug is in working order. But if no significant change is felt even after the disconnection; that means that the spark plug needs to be replaced.

Evaluate the Spark of the Spark Plug

For further verification, you can check the actual spark of the spark plug. Crank the engine to see if there is a spark in each one of your spark plug cylinders. If there is no spark; that means that the spark plug is dead. However, a weak or intermittent spark means that the spark plug is soon to wear out. In both cases, change the spark plug immediately to avoid any future engine misfires.

Make Sure that the Spark Plug is Clean

Dirt, oil or grease can cause a spark plug to miss out on proper contact. Make sure that you clean them thoroughly before testing. If performance remains the same even after cleaning, then they should be replaced.

Use a Spark Plug Tester

Testing a disconnected spark plug is different from testing it in the conditions required to run an engine. In some cases, a healthy spark from a spark plug may not be a sure indicator of a working spark plug. If you still aren’t sure about the condition of your spark plug, or simply want a more accurate gauge of your spark plug’s performance, purchase a spark plug tester. These testers recreate the conditions within the engine itself.