How to Bench Test a Spark Plug

A spark plug tester will enable you to test each plug.

At its most basic level, a spark plug is a device that starts your engine. The spark created by the plug when the key is turned on, ignites a mixture of fuel and air which gets the engine going. Bad spark plugs will prevent the engine from starting. You can bench-test each spark plug to help identify any that are malfunctioning. If the spark plugs are found to be in good working order, the problem may be the ignition instead.

Things You'll Need

• Spark plug tester

Instructions

1. Turn off the car and open the hood.

2. Disconnect the spark plug wire from the spark plug.

3. Connect the spark plug tester to the head of the spark plug.

4. Connect the clamp on the end of the tester to a piece of metal on the engine block.

5. Start the car engine.

6. Look in between the gap in the spark plug tester. If you see sparks, the plug is working. If there are no sparks, it needs to be replaced.

7. Turn off the car engine. Remove the spark plug tester and reattach the spark plug wire. Connect the tester to the next spark plug and repeat the process until all the spark plugs have been tested.

Tips & Warnings

• A spark plug tester is available at most automotive-supply stores.

References

• JacksSmallEngines: How to Use a Spark Plug Tester