An electronic dual fuel natural gas/diesel conversion system has been developed for the Caterpillar 3406 diesel engine with the Programmable Electronic Engine Control (PEEC) system. This system is microprocessor based, and interfaces with the Caterpillar PEEC system to allow control of diesel injection timing as well as fuel quantity. Control of injection timing allows pilot fuel levels as low as 3% at full load, however, to ensure good transient response, minimum pilot level is about 10%. The completed system has similar performance to the diesel engine, with comparable efficiency at full load. Furthermore, the engine's governing characteristics are similar on dual fuel or diesel only operation. Carbon monoxide and hydrocarbon exhaust emissions are higher than on diesel, particularly at light load, however, oxides of nitrogen emissions are lower.