The goal to build diesel engines achieving outstanding fuel economy and high torque output from relatively small engine displacements while lowering engine emissions produced an innovative injection technology appearing in the early 1990s. The use of hydraulic force to pressurize fuel for injection was groundbreaking technology to advance the use of cleaner, more powerful and efficient diesels engines. Hydraulically
actuated Electronic Unit Injection (HEUI) fuel systems utilize highly pressurized engine lubrication oil to drive plungers pressurizing fuel for injection. Until the development of HEUI technology, pressurization of fuel and injection timing events were controlled mechanically and limited by the fixed geometry of camshaft profiles. HEUI
systems however were the first truly modern injection system having the capability to
pressurize fuel independently of engine speed. Electronic engine control also permits enormous flexibility for engine software to optimally adjust injection pressure, fuel delivery rates and timing of the injection event for each engine speed and load condition