What is a potential consequence of an injector with a leaking o-ring?

A leaking injector o-ring can result in a variety of problems that compromise engine performance. When an injector o-ring fails, it typically causes fuel to leak out of the injector rather than being delivered to the combustion chamber. This can lead to a few noticeable consequences.

Firstly, a rough idle can occur because the engine may not be receiving the correct amount of fuel needed for optimal combustion. This leads to irregular engine operation, as the air-fuel mixture becomes imbalanced due to the uncontrolled fuel leak.

Secondly, black smoke can be emitted from the exhaust if the leaking fuel leads to a rich fuel mixture being combusted. When there's an excess of fuel, it does not burn completely, leading to unburned hydrocarbons appearing as black smoke.

Considering these outcomes, the most comprehensive understanding comes from recognizing that the implications of a leaking o-ring extend beyond just the possibility of a vacuum leak, which is more characteristic of issues related to air intake systems or gasket failures. The direct consequences include both the rough idle and potential black smoke, which can often occur simultaneously. Therefore, the most appropriate answer would point to the combined effects on engine performance caused by a leaking injector o-ring.