Over the last two decades, global emission regulations have become more stringent and have required the use of more advanced fuel injection systems. This includes the use of tighter tolerances, more rapid injections and internal components actuated by weaker injection forces. Unfortunately, these design features make the entire system more susceptible to fuel contaminants. Over the last six years, the composition of these contaminants has evolved from hard insoluble debris, such as dust and rocks, to soluble chemical contaminants. Recent research by the diesel engine manufacturers, fuel injection equipment suppliers and the fuel and fuel additive industry has discovered a major source of the soluble chemical contaminant that leads to injector deposits to be derived from cost effective and commonly used additives used to protect against pipeline corrosion. These deposits have affected engines around the world and across multiple engine sizes in diverse applications and a select few failed injectors are presented. The deposits were studied using microstructure analysis (optical and scanning electron microscopy) and detailed analytical chemistry techniques (infrared spectroscopy and elemental analysis). This paper proposes theories to explain the mechanism by which these contaminants become soluble in the fuel as well as the mechanism by which they form deposits on the metal surface and for both.