The International-Navistar 6.9-liter IDI diesel was offered from 1983 to 1987 in Ford trucks. It was the first diesel engine offered across the Ford pickup truck line. The 6.9 IDI is most commonly found in F-250 and F-350 pickup trucks.
In the early 1980s, Ford worked with International-Navistar to produce a powerful engine with better fuel economy than its 460ci gasoline engine. Ford saw a market opportunity and intended to make better use of diesel power and efficiency.
International and Ford rolled out the 6.9L V8 diesel for ¾-ton and 1-ton trucks for model year 1983. The 6.9l IDI diesel initially came with a four-speed automatic transmission or a standard four-speed manual transmission. By 1987, Ford began offering the 6.9-liter diesel with a five-speed manual transmission.
In 1988, Ford replaced the 6.9 diesel with a similar (but larger) 7.3L IDI diesel. The new engine offered greater displacement and increased power while retaining the Ford 6.9 IDI’s robust reliability. Ford continued offering IDI diesel engines in heavy-duty trucks until halfway through 1994.
Ford 6.9 IDI Specifications
The 6.9L IDI is a naturally-aspirated all-mechanical diesel engine. IDI stands for its ‘indirect injection’ fuel system, which features a mechanical rotary injection pump and mechanical injectors. Original engines never came with a turbo, but many owners added aftermarket Banks turbochargers to increase power.
||FORD 6.9L IDI
||1983 to 1987
||20.7:1 (1983) 21.5:1 (1984 to 1987)
||270 hp (3,300 RPM)
||338 lb-ft (1,800 RPM)
||10-19 MPG (EST)
The 6.9-liter IDI has a displacement of 420 cubic inches. In 1983, the engine had a compression ratio of 20.7:1, which was increased to 21.5:1 for model year 1984 and onward. The 6.9L IDI produced up to 170 horsepower at 3,300 rpm and 338 lb-ft of torque at 1,400 RPM.
Ford 6.9 IDI Reliability
Is the 6.9L IDI a good engine? Most people would say that it is. International IDI engines (in general) have a long-standing reputation for durability thanks to their mechanically simple and overbuilt design.
Other than occasional issues with head gaskets and glow plugs, there aren’t many generational issues or defects with the 6.9L IDI. However, some IDI engines suffer from overheating issues, so a well-serviced cooling system is particularly important.
6.9L IDI Diesel Performance
One downside of the 6.9L IDI is its apparent lack of power. Owners of modern computer-controlled diesels or large-displacement gasoline engines will likely be disappointed with the slow acceleration of this engine.
The easiest way to increase an old 6.9L diesel’s power output is to turn up the injection pump. Cranking up the pump can cause the engine to roll coal as well, though fuel economy will suffer. Another common modification is a Banks turbo kit, which has been popular for years. Adding a turbo is the most potent bolt-on modification in common use.