Disconnect the spark plug lead from the spark plug. Connect your spark plug tester to the spark plug lead. Connect the spark plug tester to the spark plug creating a link from the lead to the spark plug. Start the engine and watch the gap in the spark plug tester to see if there is inconsistent timing.

Can you test a spark plug with a multimeter?

An Ohm meter, which is part of a multimeter, can only check a spark plug for a short circuit or a breakdown of insulation resistance. A good spark plug should show an open circuit between the center electrode and the tip. Any resistance at all would mean the plug is bad.

What are signs of a bad spark plug?