 In 1994, due to tightening emissions regulations, the engines were redesigned to use electronically controlled unit direct fuel injection.From 1994 to 2004, the engines used HEUI (Hydraulically actuated Electronically controlled Unit Injection) injectors, co-developed by Navistar and Caterpillar Inc.. From 2004 to 2009, the engines use International's Electro-Hydraulic Generation Two (G2) unit injectors.The Navistar DT engines are currently available in three configurations.