The 1KD invisible injectors likely refers to the common rail fuel injection system used in Toyota's 1KD diesel engine. The term "invisible injectors" may be used colloquially to describe the fuel injectors because they are designed to be quieter and more efficient, thus reducing the noise and emissions associated with traditional diesel engines. In reality, these injectors are not actually invisible but rather operate in a way that makes them quieter and less noticeable during operation. They deliver fuel to the engine's combustion chamber with high precision and efficiency, resulting in improved performance and reduced emissions.