Ford originally installed a 6.9L diesel engine in their pickups back in 1982. This engine underwent some changes over the years and eventually saw an increase to 7.3 liters in 1988. This engine had some minor changes but for the most part was unchanged until 1994. 1994 saw the offerings of three different engines. The 7.3 liter of the past, a turbocharged 7.3 (both were indirect injection engines) and a new electronic 7.3 featuring direct injection and it was turbocharged (DIT for short). This new version of the 7.3 was a completely new, fresh from the ground up, engine. The only commonalities between this 7.3L and the older version was the overall displacement.
This engine achieved quite a few things and was a true leader in the industry. This was one of the first direct injection systems featuring injection pressures of up to 21,000 psi. This was achieved thanks to the rather complex Hydraulic Electronic Unit Injection system (HEUI for short). The injection system was made up of two different systems working together to achieve the pressure and performance required. The hydraulic system is a high pressure oil system that feeds the fuel injectors up to 3,000 PSI of oil pressure. The regular oil pump sends oil up to a high-pressure oil reservoir. From there, a high pressure oil pump (HPOP) pressurizes the system and sends the oil to the injectors.