This and much more helps explain why Navistar built nearly 2 million of them. It’s not uncommon to climb aboard a 7.3L-powered ’99-’03 Ford truck and find more than 400,000 miles on the clock, or an odometer that has since rolled over that (and gone back to 300,000) on a ’94.5-’97 model. Twenty-five years later, the method of injection employed on the 7.3L-though complex-remains one of the most reliable technologies Navistar and Ford ever used. However, what wasn’t so obvious at the time was how well the newfangled HEUI system, which relied on highly pressurized engine oil to make the engine run, would hold up over the long haul. With hard parts like forged-steel connecting rods and six head bolts per cylinder, the heavy-duty makeup of the 7.3L was obvious. Built by Navistar, the 444 ci V8 featured direct injection, a notable departure from its indirect injection predecessor, debuted the hydraulic electronic unit injection system better known as HEUI, provided the cleanest emissions footprint ever offered in a diesel truck and topped Dodge’s Cummins-powered, newly-redesigned Rams with best-in-class horsepower and torque figures. In an effort to stay ahead of GM at the time, but (more importantly) also gain back the ground lost with the release of the 5.9L Cummins for ’89 model year Dodge trucks, Ford released the cutting edge 7.3L Power Stroke. While General Motors didn’t offer a viable light-duty diesel engine platform until the Duramax came along in 2001, Ford all but revolutionized the segment in 1994.