Method of determining the composition of fuel in a flexible fueled vehicle with an O2 sensor

A method for controlling combustion parameters of an internal combustion engine in a flexible fueled vehicle with an oxygen sensor prior to a closed loop operating condition comprising:

• determining if newly added fuel has started to blend with old fuel in a fuel system of said vehicle;
• determining possible blend ratios of ethanol and gasoline based on a volume of said newly added fuel and a percent alcohol content of said old fuel;
• determining if a lean operating condition exists;
• determining if a rich operating condition exists;
• incrementing a percent alcohol content value based on a first of said possible blend ratios if said lean ratio condition exists;
• decrementing said percent alcohol content based on a second of said possible blend ratios if said rich ratio condition exists;
• and
• setting said combustion parameters according to said percent alcohol content.