Automobiles, which are built to operate with gasoline and equipped with port fuel injection (PFI) spark ignition (SI) engines, can be converted to use ethanolgasoline blends, such as commercially available E85. Fuel conversion allows using a sustainable source of fuel. Gasoline and E85 have different chemical and physical properties. Use of E85 increases the engine power output and reduces emissions of hydrocarbon and carbon monoxide components in the exhaust gases. The negative aspects of use of E85 are engine cold start difficulties, chemical aggression, increased emission of aldehydes and increased fuel volume consumption. This study focuses on revealing the specific properties of the fuel injectors, which are becoming particularly important when selecting injectors for automobiles within the process of fuel conversion. Electric and acoustic injector diagnostic methods are described. The results of this research can be practically applied when fuel injectors are being evaluated or selected for the fuel conversion purposes.