If a spark plug wire falls off while the engine is running, what happens to HC emissions at the tailpipe?

When a spark plug wire falls off while the engine is running, it leads to a misfire in the affected cylinder. Spark plugs are responsible for igniting the air-fuel mixture in the combustion chamber; without a proper ignition, that mixture fails to combust fully. This incomplete combustion contributes to an increase in unburned hydrocarbons (HC) in the exhaust gases.

Hydrocarbon emissions are a byproduct of the combustion process. If there is misfiring due to a disconnected spark plug wire, the unburned fuel gets exhausted directly into the tailpipe, resulting in higher HC emissions. The system may still be operational for other cylinders, but the overall emission from the tailpipe will increase as more hydrocarbons escape unburned.

Therefore, the correct answer is that HC emissions at the tailpipe will increase due to the misfire caused by the spark plug wire falling off.