Patent ID: 8903626

Claim:
A method of adjusting a fuel composition estimate for a vehicle, the method comprising: sensing a refueling event; after sensing the refueling event, determining whether an air-fuel ratio sensor is operable to provide an updated estimate of fuel composition; and providing an updated fuel composition estimate if the air-fuel ratio sensor is not operable, including performing steps comprising: monitoring estimated engine torque to determine whether first variations in engine torque over a first period after the refueling event exceed a threshold; and modifying a previous first fuel composition estimate prior to the refueling event by a first pre-determined amount to determine a second estimate of fuel composition if the first variations in engine torque exceed the threshold after the refueling event and while the air-fuel ratio sensor is not operable for providing an updated fuel composition estimates; the method further comprising: modifying the second estimate of fuel composition by a second amount if, after performing the step of modifying the first estimate of fuel composition by the first pre-determined amount, second variations of engine torque again exceed the threshold; and wherein the step of modifying the second estimate of fuel composition by the second amount comprises: comparing the first variations in engine torque prior to a first correction with the second variations in engine torque occurring after determining the second estimate of fuel composition for the first correction; and modifying the second estimate of fuel composition by a second pre-determined amount that is substantially the same as the first pre-determined amount to obtain a third estimate of fuel composition if the first variations and the second variations are substantially the same.