Caterpillar Inc. has developed a new diesel engine fuel system, powered by hydraulics and controlled electronically. This Hydraulic Electronic Unit Injector, (HEUI), requires no mechanical actuating or mechanical control devices, and offers many advantages over conventional fuel injection systems.Inherent features of the HEUI Fuel System include injection pressure control independent of engine load or speed, totally flexible injection timing, and full electronic control of injection parameters. Packaging the HEUI Fuel System on an engine is simple, as the injector is compact and available in a variety of configurations. The hydraulic actuating circuit is straightforward, using lubricating oil from the engine sump. Hydraulic lines may be internal to the engine or external.This paper describes the Caterpillar HEUI Fuel System, its operating features, performance advantages, and application to diesel engines. System performance is compared to conventional mechanical and electronic unit injected fuel systems. HEUI characteristics are also compared to future fuel system requirements of the diesel engine as determined by a Quality Function Deployment (QFD) process.