They were even running a prototype Kenworth at Pikes Peak a couple years ago.
I think Sturman patented his digital valve sometime in the 70's or 80's, originally for irrigation systems
In the early 90's they got a contract with Navistar to install their valves in the injector systems on a number of their truck engines. As I recall, they were talking of thousands of engines.
The valve allowed for a microsecond burst of a very small amount of fuel, a slight pause to allow ignition to begin, and then the injection of the 'power' shot of fuel. That increased fuel efficientcy, and cleaner burning.
Pretty amazing when that all happens everytime the piston reaches the begining of the power stroke.