Methods and systems for determining an LPG fuel output characteristic of an LPG injector. The output characteristic of the LPG can be determined by calculating a total mass of LPG injected into a canister of known volume by the injector during a plurality of open/closed cycles of the injector. The pressure differential and temperature in the canister can be used in the calculation of total LPG mass along with a gas constant of the LPG and the volume of the canister. The total LPG mass can then be used to determine the mass of LPG injected by the injector during each open/closed cycle.