Testing spark plugs can help you determine the condition of your ignition system. If your engine is running roughly, skipping or missing, a great place to start is the spark plugs and wires. Testing the spark plugs is quick and simple, requiring only a spark plug tester available at any auto parts store. A good spark plug tester will allow you to see if there is spark to a cylinder, determine the quality of the spark and work safely while testing your ignition system.
Remove the spark plug wire from the spark plug on one cylinder. It is best to take off each plug wire one at a time so as not to mix them up.
Insert the long end of the spark plug tester onto the spark plug, and plug the other end into the boot on the spark plug wire. Do not set the wire on anything hot, such as manifolds or other engine parts.
Start the vehicle and observe the spark in the window of the tester. If there is no spark, check the connections on the tester and the plug wire at the distributor.
Replace the plug if no spark is present and retest. If you still do not have spark, you will need to check the wires and distributor.
Test each plug, changing any that may be faulty with a new spark plug. Be sure to check the recommendations of the vehicle manufacturer for the correct spark plug application.
Do not handle the wires while the car is running. The ignition system uses extremely high voltage and can be dangerous if not handled properly.