The goal of the present work is to develop an open architecture engine controller to operate a production model, heavy-duty diesel engine. Where OEM engine control units (ECUs) are inflexible, this controller is designed to provide the hardware and software flexibility required to facilitate dualuel combustion research. This thesis includes thorough descriptions of the hardware and software development required to interface with all engine sensors and actuators. To establish baseline control settings for the open controller, OEM ECU responses are mapped over a range of speeds and loads. This information is used to calibrate the open controller. Comparison tests considering speed, load, and emissions are performed to ensure the open controller provides a close approximation of OEM engine operation. The results of the tests confirm that the open controller provides full control of the engine with baseline settings close to those of the OEM ECU.