A dedicated closed-loop propane fuel system has been developed for the General Motors Medium Duty truck with a 7.4 liter engine. The fuel metering system consists of a closed-loop controlled regulator and mixer. Regulator output pressure is controlled by a pulse-width modulated vacuum signal from the mixer for off-idle operation. Idle fuel is provided by an electronically controlled, fuel metering solenoid valve. Additionally, original equipment manufacturer (OEM) fail-safe performance of the Electronic Throttle Control system has also been achieved. This fuel system is an example of how an open loop regulator-mixer system can be enhanced with electronic controls to achieve significant improvements in emission signature, driveability, and customer satisfaction.