A faulty coil may fire intermittently, produce a weak spark or kill a cylinder completely. Coils are sensitive to heat and may produce an intermittent problem if their internal components become weak. Once the winding inside weakens or breaks, the problem is irreversible. However, you can test the coil pack on your car using a voltmeter.
Park your car in a safe place and open the hood.
Locate the coil pack in your engine by following the spark plug wires from the spark plugs; the wires are connected to the coil pack. Depending on your particular vehicle model, you may find the coil pack mounted on one side or the back of the engine.