Article describes diagnose and research methods Common Rail system fuel injectors. Professional diagnose modern fuel injectors is very difficult procedure. Basic theirs work parameter influencing on correctly work parameters are magnitude injection and return dosages by definite pressures prevailing in system and injection times. Sometimes dosages during diagnose by coordinate task and actual fuel injector are correct but engine work is not proper. So that during diagnose should extend tests procedure in range varies work conditions. Fuel injectors work characteristics are one of method researching in whole range work. During researches has been used Continental fuel injector.