How do you check if cylinders are firing?

To check if cylinders are firing, you can use an ignition timing light or a cylinder compression tester. With an ignition timing light, you can observe the flash of the light at the spark plug wire to see if it is firing. A compression tester will measure the pressure in each cylinder; if a cylinder has low or no compression, it may not be firing properly. Additionally, you can visually inspect spark plugs for wear or fouling and listen for engine vibrations or misfires while running.