In 1981 Ford signed an agreement with International Harvester to produce diesel engines for their light truck line. This led directly to the production of the 6.9-liter IDI diesel. The engine is developed as a low cost, light weight diesel that fit where a V8 gas engine would, to try to convert their gas engine customers to diesel and to sell to Ford for use in F-Series light duty trucks and E-Series/Econoline vans. Before it could be sold to Ford however, Tenneco Inc. purchased in the "Harvester" division of International Harvester which was moved within their Caseheavy equipment line. The remainder of what was International Harvester was renamed Navistar, which concentrated on engine and medium/heavy truck development. Consequently, these are actually International-Navistar IDI engines.
6.9L
During the 1983 model year, the F250 and F350 trucks were first available with the 6.9L diesel engine. This was the first diesel engine offered in Ford light-duty pickups. Although the GM pickups already had offered a diesel engine in C10s starting in 1977, and C10-30 in 1982, the GM diesel engines were intended for efficiency over power. The 6.9 L loosely replaced the gas V8 that was offered between 1977 and 1982. The 6.9 was billed as a fuel efficient alternative to the V8 Windsor gasoline engine. Falling between the base Inline-6 and top-of-the line gas V8, the 6.9 L engine was naturally aspirated and put out @ 3,300 RPM and @ 1,400 RPM.
7.3L
In 1988, the 6.9-liter engine was supplanted by the 7.3-liter upgrade, with over 300,000 6.9's shipped to Ford and countless numbers installed into medium-duty trucks, school buses, and the like. This engine features numerous improvements over the 6.9-liter, with most of the changes located in the heads; the block received an increase bore and select-fit pistons, while the heads received an enlarged prechamber, enlarged valve stem shields, harder valves, and other minor upgrades. The front cover was revised to reduce seepage. The 1st 7.3l-liter engine was introduced in 1986 for the International s-series trucks & school buses, The 6.9-liter and the 7.3-liter engine was an optional for International s-series trucks and school buses from 1986-1987 before it went straight to the 7.3-liter engine in 1988 for Ford trucks and International trucks and school buses until the end of the 1994 year model. Finally, in 1993 Ford made available a turbocharged edition of the 7.3 L. An internally wastegated, AR.82 Garrett T3 series turbo was used as the OEM for the factory turbocharger system. The system was tuned to minimize performance loss at high elevation, rather than to improve peak performance. A primary limiting factor to the performance potential of the engine is an incredibly restrictive stock down-pipe. It is commonly believed, but not officially verified, that this is deliberate and due to Ford's impending release of the T444E engine. Factory turbo vehicles received numerous additional improvements. Pistons had an enlarged primary compression ring, added intermediate ring, an enlarged ring land and wrist pin, as well as an anodized piston face. Other improvements included tweaks to the injection pump, and an upgraded oil-coolant heat exchanger.
Fuel system
These engines use an injection pump that is entirely mechanical, this was the standard for diesels of the day. The fuel system also utilizes indirect injection which made it quieter than mechanically direct injected engines. Both 6.9 and 7.3-liter engines use the Stanadyne DB-2 injection pump fed by a cam-driven lift pump.
