The fuel system used a very straightforward and reliable Stanadyne rotary distributor inje
IDI Fuel System
IHC used a Stanadyne DB2 rotary distributor fuel injection pump that incorporated a hydraulic speed advance and a light load advance for optimum timing over the entire operating range.
Additional advance was achieved during cold starting and warm-up to reduce white smoke and hydrocarbon emissions. A solenoid controlled by a thermo-switch in the cooling system unseated the ball valve of the housing pressure regulator. This reduced housing pressure, which allowed a greater amount of injection advance for the given load and engine speed.
The governor was a minimum/maximum design, providing control action in the low idle speed range and above the rated speed. Between these ranges, the throttle lever controlled the metering valve position. A snubber orifice machined into the distributor rotor indexed with the ports in the head after the main injection took place. The damper orifice reduced aftershocks in the injection lines and eliminated unwanted secondary injections of fuel.
Outward opening poppet nozzles were tested first with a 30-degree angle toward the swirl chamber wall and a smaller hole spraying 10 percent of the fuel toward the glow plug. Performance with this design was satisfactory, but hydrocarbon emissions were high and coking of the small 0.009-inch orifice proved to be a problem. As a result, inward opening pintle nozzles were developed to fit in the space confines of the 0.67-inch orifice nozzles. Performance, emissions, and durability all proved to be excellent with the new design-and nozzle coking was kept at a minimum.
The fuel system was mounted on the engine and included a mechanical fuel lift pump, inline fuel heater, and a fuel filter prior to the injection pump. A constant bleed orifice was used on the outlet of the fuel filter to eliminate the need for hand priming or manually bleeding the air from the system when the filter was changed or the tank was allowed to run dry.
An electrically activated glow plug was used in each swirl chamber to improve starting below 70 degrees Fahrenheit. The glow plug temperature was controlled by an electromechanical bi-metallic switching device, which pulsed 12 volts to the 6-volt glow plugs. The initial energized period of up to 10 seconds pre-glow produced glow plug temperatures that provided acceptable engine starting to minus-10 degrees. The system incorporated an after-glow feature that continued to activate the glow plugs for a period of about 1 minute after the engine started. This feature reduced the amount of white smoke developed on cold start until the combustion chamber walls were sufficiently heated. For starting below minus-10 degrees, a 110-volt electrical block heater was provided.
A Successful Design
The 6.9L engine underwent extensive development and durability testing before the start of production. A total of 160 prototype and 10 pre-production engines were built for engineering tests. The test engines had accumulated a total of 52,000 laboratory durability test hours and 815,300 miles of field tests by the time Ford vehicle production began.
The laboratory tests included:* 21,000 hours at full load
* 16,500 hours at 72 percent load
* 4,500 hours of special durability tests
* 10,000 hours on pre-production engines
The 10 pre-production engines were built and tested on the dynamometer to verify the quality of the production process. Each engine was subjected to 1,000 hours (approximately 80,000 miles) at full load, with no problems occurring. In addition, pre-production engines were placed in customer fleet trucks and subjected to varied conditions, drivers, and use.