Lisle ignition spark testers are the best way to check ignition spark without removing the spark plug. Specially calibrated to measure ignition voltage, they work on both standard and electronic ignition systems. The testers are easy to use, utilizing an adjustable calibration screw to be moved to the proper gap size. Simply attach the spark plug wire to the end of the tester, clamp the tester onto the engine ground, and crank the engine to test for spark. They're available in several styles for use on various types of spark plugs.