What identifying factor can suggest issues with a vehicle's fuel injectors?

High hydrocarbon emissions during testing can indicate issues with a vehicle's fuel injectors. Injectors that are malfunctioning can either deliver too much fuel (leading to a rich fuel mixture) or too little fuel (causing a lean condition). When too much fuel is introduced into the combustion chamber, it can lead to incomplete combustion, resulting in an increase in unburned hydrocarbons being emitted from the exhaust. This is why elevated hydrocarbon levels are a significant indicator of fuel injector problems.

While poor acceleration and unusually high RPM readings can also point towards fuel system issues, they are not as definitive for indicating injector malfunctions as high hydrocarbon emissions. Poor acceleration could be caused by various factors, including transmission issues or other engine problems, and high RPM readings could suggest an unrelated issue with engine timing or other components. Thus, high hydrocarbon emissions serve as a more direct signal that a vehicle's fuel injectors may not be operating correctly.