Can a bad spark plug cause a car not to start? Yes. The spark plug ignites the fuel/air mixture inside the cylinder. If the fuel doesn’t burn, the engine doesn’t make power. This results in reduced power, and makes the engine produce power unevenly. The more cylinders your engine has, the easier it is to start the car with one bad plug. That’s because the ignition cycles in the other cylinders keep the crankshaft spinning. If you have a three or four cylinder engine, there’s a large gap in power between successful ignition cycles, making it harder to start.
