This paper describes the conversion of a stationary spark ignition engine to a heavy duty (HD) natural gas engine suitable for transportation applications, in response to the new urban truck and bus legislation of 1994 and 1998. The approach to the fuel and ignition control system is to use a microprocessor controlled engine management system based on inputs from combustion air and natural gas mass flow sensors. As the emission control system is also based on stoichiometric three way catalyst technology, it is felt that the control approach is very robust.The engine and control system were first mounted on a HD dynamometer for the development work where engine control parameters were calibrated. In addition steady state emission data were collected and estimates of the HD transient emission levels were obtained.The engine and control system were then subsequently transferred to a specially prepared class 7 dump truck chassis, based on the Kenworth T800, which had been fitted with suitable natural gas storage. The truck is now in daily usage with a city public works department in western Canada, and is under periodic monitoring by the authors.