Which of the following is a key sign of a failing fuel pump?

A key sign of a failing fuel pump is difficulty starting the engine. The fuel pump's primary function is to deliver fuel from the tank to the engine at the correct pressure. When the fuel pump begins to fail, it may not adequately supply fuel, leading to hard starting or even engine stalls. This issue can manifest as a long cranking time when starting, or the engine may not start at all if the fuel pump fails to deliver fuel properly.

While engine overheating, poor fuel economy, and exhaust smoke can indicate other engine problems, they are not direct indicators of a failing fuel pump. These issues could be caused by various factors, such as cooling system failures, fuel mixture problems, or combustion-related issues. Therefore, recognizing difficulty starting as a sign of a failing fuel pump is crucial for diagnosing and addressing fuel delivery problems effectively.