During engine diagnostics, what does a consistently high reading of unburned hydrocarbons (HC) in the exhaust gas indicate?

During engine diagnostics, a consistently high reading of unburned hydrocarbons (HC) in the exhaust gas indicates incomplete combustion. Unburned hydrocarbons are fuel molecules that did not fully oxidize during the combustion process in the engine cylinders. A high HC reading signifies that fuel is escaping the combustion chamber without being burned. This can be caused by several factors. These include: a misfiring cylinder (due to a faulty spark plug, ignition coil, or fuel injector), low cylinder compression (caused by worn piston rings or damaged valves), an overly rich air-fuel mixture (too much fuel and not enough air), a malfunctioning oxygen sensor, or a problem with the catalytic converter (which is designed to further oxidize hydrocarbons). For example, if one cylinder isn't firing properly, the fuel injected into that cylinder won't burn, resulting in a high HC reading. Similarly, worn piston rings can allow fuel and air to leak past the rings, reducing compression and leading to incomplete combustion. The specific acceptable HC level will vary depending on the engine type, emission standards, and testing procedure, but a reading significantly above the manufacturer's specified limit indicates a problem that needs to be addressed to prevent poor engine performance, increased fuel consumption, and excessive emissions. Further testing is required to determine the root cause of the high HC reading and implement the appropriate repairs.