The paper describes the methodology and results of evaluation of the flow capacity of the fuel injectors in the automobiles, equipped with spark ignition, port fuel injection engine. Automobiles, which are designed to work with regular gasoline, can be adapted for use of blend of bioethanol and gasoline, for instance, fuel E85. Certain components have to be evaluated for their compatibility with E85. The fuel injectors of the adapted engine have to supply a larger amount of E85 fuel, comparing with the operation with gasoline. The studies were conducted on two unmodified automobiles. The tests were performed on a roll type chassis dynamometer, set in constant speed mode. The measurements were done using a multichannel oscilloscope and piezoelectric microphone. Combined electrical and acoustic injector diagnostic methods were used and are thoroughly explained. The obtained results confirm the efficiency and robustness of the chosen diagnostic method. The results of the automobile testing confirm the necessity of the injector flow evaluation before converting the automobile for use of E85 fuel.