Which of the following symptoms may indicate a problem with the fuel system?

Engine misfiring or stumbling is a common symptom that may indicate a problem with the fuel system. This issue often arises when there is a disruption in the fuel delivery to the engine, which can be caused by various factors such as a clogged fuel filter, a failing fuel pump, or issues with the fuel injectors. When the engine does not receive the correct amount of fuel, or the fuel being supplied is not atomized properly, the combustion process becomes erratic, leading to misfires or irregular engine operation. These manifestations are closely tied to the performance of the fuel system, making this symptom a clear indicator of potential fuel-related issues.

Other options, while they may indicate their own distinct problems, do not directly relate to the fuel system's performance. Excessive exhaust smoke may point to issues such as oil consumption or coolant leaks, uneven tire wear typically indicates alignment or suspension problems, and worn brake pads are clearly a braking system concern. Thus, misfiring or stumbling is the only symptom directly connected to fuel system malfunctions.