Method of operating a fuel injector of an internal combustion engine

Disclosed is a method of operating a fuel injector 160 of an internal combustion engine 110. The method comprises the steps of performing a first test injection with a first test energizing time, measuring an actual fuel quantity that has been injected during the first test injection to obtain a first point (C1, R1) of a characteristic curve (B, C) representing a relationship between the energizing time applied to the injector 160 and the fuel quantity which is actually injected by said injector 160. A ratio between the actual fuel quantity injected and a nominal fuel quantity corresponding to the first test energizing time (CI) is calculated. The calculated ratio (Ratio x) is used to determine a plurality of corrected energizing times (Cx) for subsequent test injections. The subsequent test injections are performed using the corrected energizing times (Cx) and the actual fuel quantity (Ry) that has been injected during each one of the subsequent test injections are measured to obtain further points (Cx, Ry) of the characteristic curve (B,C). The characteristic curve (B,C) of the fuel injector 160 is modeled on the basis of the obtained further points (Cx, Ry) and the characteristic curve (B, C) is used to control the operation of the fuel injector 160. An associated apparatus, automotive system, computer program and a control apparatus are also disclosed.