A variety of strategies have been developed over the years for controlling engine speed in an internal combustion engine. Engine speed is commonly expressed in crankshaft revolutions per minute, or RPM. In one known strategy, a fueling map where fueling signal duration is mapped to requested engine speed is populated when an engine is assembled and tested at a factory, or otherwise prior to being placed in service. Such engine fueling maps typically define an on-time for a fuel injector electrical actuator which is mapped to an engine speed request expressed in RPM. Accordingly, an operator or engine control system can utilize an input device to request a specified speed, and the associated engine control system determines a fueling signal duration which corresponds to the requested engine speed. While such a strategy provides a relatively straightforward means for controlling engine speed, it has long been recognized that closed loop control will tend to enable a control system to achieve a desired engine speed more rapidly and in a generally automatic fashion. In a typical closed loop engine speed control strategy, and engine speed sensor outputs sensor signals indicative of a rotational speed of an engine crank shaft, fly wheel, etc., and a computer compares the sensed engine speed with the requested engine speed and responsively outputs an engine speed error signal. The computer will loop through a control routine numerous times, outputting fueling signal commands refined according to the engine speed error signal until the requested engine speed is achieved.
As mentioned above, conventional engine speed control strategies rely upon map data determined under a given set of operating conditions prior to placing the engine in service. Engine fueling maps may be updated periodically throughout a service life of an engine by running diagnostics and the like. Diagnostics are typically performed to compensate for changes in engine behavior which result from breaking in of the engine, in particular mechanical wear of certain components and changes in component responsiveness. Changes in fuel injector performance an variation among fuel injectors in performance over the course of an engine's service life will be familiar to those skilled in the art. Various electronic trimming strategies and fuel injector performance diagnostics to identify faulty injectors are also well known. Conventional strategies for addressing changes in fuel injector performance, or general unpredictability of fuel injector performance among a group of injectors of a given fuel system, have various drawbacks.