Methods and systems are provided for enabling a transfer function of a direct injector and a port injector, each fueling an engine cylinder, to be accurately learned. During selected conditions, the direct injected fuel fraction may be actively changed from a target fraction to one of an upper and lower limit of the direct injector so as to provide a measurable air-fuel ratio error. Fueling errors for the distinct fuel injectors is then learned based on the measured air-fuel ratio error relative to the actively changed fuel fraction.