Which test would likely help identify issues with fuel injection efficiency?

Air-fuel ratio monitoring is crucial for determining fuel injection efficiency because it measures the balance between the amount of air and fuel being mixed and delivered to the engine. An optimal air-fuel ratio is essential for efficient combustion; deviations can indicate problems with fuel delivery, such as insufficient fuel being injected or an excess that can lead to incomplete combustion. This monitoring enables technicians to diagnose issues that affect engine performance, fuel consumption, and emissions.

In contrast, while exhaust gas analysis can provide information about combustion efficiency and emissions, it is not as direct a measure of fuel injection efficiency compared to monitoring the air-fuel ratio. Fuel temperature measurement relates to the physical properties of the fuel but does not give insight into how effectively the fuel is being injected. Battery voltage checks primarily assess electrical supply issues and do not directly relate to the efficiency of fuel injection systems.