What can occur if an injector becomes clogged?

A clogged injector can lead to several consequences that significantly impact engine performance. When the injector is blocked, the fuel delivery to the engine becomes irregular. This inconsistency can indeed cause decreased fuel efficiency because the engine may not receive the optimal amount of fuel needed for efficient combustion. As a result, the engine struggles to maintain power, leading to excessive fuel consumption for the same performance.

Moreover, a clogged injector can alter the combustion process, which can result in incomplete burning of fuel. This incomplete combustion can, in turn, lead to higher emissions being released into the atmosphere. Engines that do not burn fuel completely create more hydrocarbons and other harmful pollutants.

The clogging can also affect the air pressure in the fuel system. The fuel system may struggle to maintain the necessary pressure if the injector is not allowing fuel to flow smoothly, which can lead to increased air pressure within the system as a side effect.

Thus, all of these factors—decreased fuel efficiency, increased air pressure, and higher emissions—can occur due to a clogged injector, making the comprehensive answer of "All of the above" correct.