ASE Engine Performance (A8) Practice Test 2025 - Free Engine Performance Practice Questions and Study Guide

A common sign of a malfunctioning fuel injector is engine stalling or rough idling. This occurs because faulty fuel injectors can fail to deliver the proper amount of fuel to the engine, leading to an improper air-fuel mixture. When the mixture is not correct, the engine may struggle to maintain a smooth and consistent idle, which can cause it to stall or run roughly. This symptom can arise from various injector issues, such as clogging or leaking, all of which disrupt the proper fueling of the engine.

In contrast, optimal fuel economy, increased engine power output, or decreased exhaust smoke are indicators of good engine performance and effective fuel injector function. If the fuel injectors are malfunctioning, one would typically see reduced fuel efficiency, potentially lower power output, and possibly an increase in exhaust emissions rather than a decrease. These factors help distinguish the presence of injector issues from a properly functioning fuel system.