Abstract: A test instrument for measuring the injection time of different types of electronic fuel injectors in a fuel injected engine is provided. The test instrument is coupled to receive an injection signal from any of a variety of fuel injector types and over a range of injection times and repetition rates. The injection signal is digitally sampled and stored in memory. The injection time is determined according to an algorithm executed by a microprocessor which operates on the stored injection signal to determine first and second edges, with the time difference between the first and second edges representing the injection time. The second edge must be followed by the injection signal being substantially equal to the battery voltage for a predetermined hold time in order to reject false edges occurring before the second edge.