Hydraulic Electronic Unit Injection......HEUI
Basically hydraulic oil pressure from a separate HP oil pump that shares its oil with the crankcase...which does explain why powerstrokes take more oil than GM and Dodge does and the system can be brought to its knees if the wrong viscosity is used (no start in colder climes) and services must be religiously followed or the HP oil pump fails, can stick an injector open...bye bye piston/Engine.
Everything you wanted to know but were afraid to ask can be found
HERE