Firing order is:

• A. The numerical sequence in which cylinders fire
• B. The order of spark plug replacement
• C. The sequence of valve openings
• D. The movement of pistons in the engine

Answer: (A)

The firing order is the numerical sequence in which the cylinders fire, meaning the timing of ignition events that produce power in each cylinder. In a multi-cylinder four-stroke engine, each cylinder fires once every two crankshaft revolutions, and the order is chosen to distribute power pulses evenly and minimize vibrations. It’s about when each cylinder ignites, not about which spark plugs you replace, the timing of valve openings, or the physical movement of pistons. The valve timing and piston movement are related to how the engine breathes and rotates, but they are separate from when each cylinder actually ignites.