In the long run, the 6.9L would prove to be dependable and superior in longevity to its primary competition of the era. The 6.9L IDI was backed by either a T-19 4 speed manual or C6 3 speed automatic transmission, with the exception of some rare ZF S5-42 5 speed manual transmissions in the 1987 model year. It was eventually replaced by the 7.3L IDI, which is essentially a redesigned, bored over, higher output version of the engine.
6.9L IDI Diesel Specs
| Manufacturer | International Harvester |
| Production Years | 1983-1987 (for Ford Trucks) |
| Applications | Ford F-250, F-350, F-Super Duty |
| Configuration | V-8 |
| Firing Order | 1-2-7-3-4-5-6-8 (stamped on intake manifold) |
| Cylinder Numbers |  |
| Block/Head | • Cast iron engine block • Cast Iron heads, 7/16" head bolts |
| Displacement | 420 cubic inches, 6.9 liters |
| Compression | 20.7:1 (1983) 21.5:1 (1984+) |
| Bore | 4.00 inches |
| Stroke | 4.18 inches |
| Injection | indirect injection (IDI), mechanical, Stanadyne DB-2 rotary pump |
| Aspiration: | Naturally aspirated, non-turbo |
| Oil Capacity | 10 quarts w/ filter |
| Weight | ~ 990 lbs |
| Horsepower | 155 - 175 hp @ 3,300 rpm depending on factory injection pump calibration. There were also separate calibrations for high and low altitude applications. |
| Torque | 318 lb-ft. @ 1,400 rpm |
1984 model year and newer engines received a higher compression ratio than the introductory engine. Pre-84 engines are referred to as "A" model engines, while the later was designated the "B" model. All engines with serial number 59209 and greater were model B engines. In addition to the increased compression ratio, B model engines had an alternate exhaust valve and prechamber insert design (smaller prechamber). The piston height was increased by 0.003" to achieve the higher compression ratio, and the piston design also had an enlarged cup to promote a more efficiency swirl.
The 6.9L IDI was ultimately successful in competing with GM's 6.2L Detroit diesel, which was designed specifically as an economical alternative to their line of gas engines and not a heavy hauler. The 6.9 proved more reliable and more conducive to the true purpose of owning a diesel than their competition. To respectfully judge the 6.9L IDI today, it is impossible to compare to modern diesel engines. If nothing else, the 6.9 was technologically limited, as it was completely mechanically controlled, naturally aspirated, and was developed at a time when diesels were not in the horsepower/torque race that they have been in more recent times. It is quite common to turbocharge the 6.9 via aftermarket kits. While this greatly enhances performance an can even improve fuel economy, the only safe way to do so without challenging the engine's reliability or longevity is to run conservatively low boost pressures and properly calibrate the injection pump.