If a weak cylinder is found during a compression check, which component must be inspected first?

When a weak cylinder is detected during a compression check, the first component that should be inspected is the piston rings. Piston rings play a critical role in maintaining cylinder compression by sealing the combustion gases within the cylinder. If these rings are worn, damaged, or improperly seated, they can allow gas to escape, leading to reduced compression readings.

Inspecting the piston rings first is logical because they directly affect the cylinder's ability to hold compression. If the piston rings are the problem, other components, such as the cylinder itself or the valves, might also be affected, but the rings are a common issue that directly influences the measurements seen in a compression test. Evaluating the condition of the piston rings can lead to a more accurate diagnosis of the weak cylinder's cause and facilitate the appropriate corrective measures.

Other components listed might relate to engine performance, but they do not have the same immediate and direct impact on cylinder compression as the piston rings do. For example, while fuel injectors can affect the overall engine operation by influencing the air-fuel mixture, they do not contribute to the cylinder's ability to hold compression. Similarly, timing belts impact valve timing and, indirectly, engine performance, but they are not typically the first suspect in a compression issue.