What might cause an engine to run too rich or too lean relative to injection?

An engine running too rich or too lean is primarily influenced by the injector performance and fuel delivery system. Faulty injectors can cause an excessive or insufficient supply of fuel, leading to an imbalance in the air-fuel mixture. If injectors are not functioning correctly, they may either dribble too much fuel into the combustion chamber (causing a rich condition) or fail to deliver enough fuel (resulting in a lean condition). Similarly, incorrect fuel pressure can disrupt the intended fuel delivery to the engine, affecting the efficiency of combustion.

Factors like clean fuel injectors, a proper air-fuel mixture, and functioning fuel filters typically contribute to optimal engine performance rather than causing a rich or lean condition. Clean injectors ensure that fuel is delivered accurately, proper air-fuel mixture indicates that the proportions are balanced as intended, and working fuel filters prevent contaminants from affecting fuel quality. Therefore, while those factors are crucial for maintaining engine performance, they do not directly cause the rich or lean conditions associated with improper fuel injection.