Abstract: A diesel engine (10) wherein both the operating speed of the engine (RPM) and the timing of the fuel injection into the engine (AA) are cooperatively controlled to be responsive to both the temperature and the pressure of the air (30) used for combustion. A controller (44) receives a temperature signal (28), an air pressure signal (36), and a power demand signal (24) and executes control logic to produce a fuel injection control signal (46) and an engine speed control signal (48) for controlling a fuel injection system (16). A control strategy based on engine inlet air temperature and pressure or manifold air density may be useful for variable speed and power applications. For applications with discreet speed and power points, such as a locomotive, a speed and timing control strategy based on ambient temperature and pressure is useful for maximizing power during high altitude and/or high ambient/inlet air temperature operation.