A method for testing a fuel injector including providing an engine with a common rail fuel injection system having one or more fuel injectors; operating the engine at a selected set of operating conditions; conducting a motoring event; allowing a first settling duration; measuring a first rail pressure; operating a first selected injector including operating the first selected injector singly in response to a selected fuel quantity, a selected number of combustion cycles, and a selected number of injections per combustion cycle; allowing a second settling duration; measuring a second rail pressure; calculating a pressure difference value in response to the first rail pressure and the second rail pressure; inferring an amount of fuel delivered by the first selected injector in response to the pressure difference value; and evaluating a first performance factor of the first selected injector in response to the amount of fuel delivered.