Compressed natural gas has been largely regarded as a clean fuel for vehicle application, and is being increasingly used in the industry to reduce pollution and as an alternate fuel to gasoline & diesel. CNG has the potential to reduce emissions, provide greater fuel efficiency and reduce import costs. Moreover, it is more economical as compared to other fuels.CNG injection technology was developed with the aim of providing improved emissions and performance equivalent to gasoline engines by better control in fuel metering. Consistent efforts are being made to improve the performance of the injectors by doing design changes and value engineering for improved injection performance, noise reduction etc. New improved injectors can be implemented in the existing system with minimum effort by thoroughly studying the design differences of the injectors. This paper describes an approach that helps to reduce calibration effort resulting in reduction of development time of CNG models while implementing improved injectors in the existing system. This paper also describes the parameters to be considered for engine control unit (ECU) calibration after studying the design differences between the old and improved CNG injectors. This paper also presents a case in which experimental data validates the on-desk calibration approach.