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.