Which of the following relates to the fuel system if the engine runs too lean?

When an engine runs too lean, it means that there is too much air in the air-fuel mixture relative to the amount of fuel being delivered. This improper air-fuel mixture can cause various issues, such as increased engine temperatures, misfires, and potential damage to engine components due to knock or pre-ignition.

The fuel system is crucial because it is responsible for delivering the appropriate amount of fuel to achieve an optimal air-fuel mixture for combustion. If the ratio is off, as in the case of a lean condition, it's typically indicative of problems like a malfunctioning fuel injector, a failing fuel pump, or an air leak that allows excess air into the system without the corresponding increase in fuel.

In contrast, excessive fuel delivery is related to a rich mixture, not a lean one, while increased acceleration and better fuel economy are outcomes usually associated with a well-tuned engine rather than directly indicating issues with the fuel system when the engine operates lean. Therefore, the relationship of the fuel system's quality with the air-fuel mixture becomes evident when diagnosing lean operation conditions.