What is the effect of an injector stuck open?

When an injector is stuck open, it continuously allows fuel to flow into the combustion chamber, regardless of whether the engine is actively firing. This constant fuel flow leads to an overly rich mixture in the combustion chamber, which can result in flooding. Flooding occurs when there is too much fuel and insufficient air for combustion, leading to poor engine performance, excessive emissions, and potential for engine starting difficulties.

In this scenario, while other effects like intermittent fuel supply or improved efficiency could be associated with injector issues, a stuck open injector indisputably creates a situation of continuous fuel flow. This characteristic distinctly defines the primary impact of such a malfunction, making it the correct answer.