Fuel injector signals have a few different characteristic shapes. The majority of injectors are ground controlled. Voltage is supplied to the injector when the ignition is on and the PCM controls the injector on time by completing the circuit to ground. There are a few manufacturers that turn the injector on by supplying voltage through the PCM. All of the graphic examples in this set are typical good signals. Fig 1, saturation injector, Fig 2, Peak and Hold injector, Fig 3 Peak and frequency modulated hold and Fig 4 Peak and frequency modulated hold, (PNP driver); this injector is normally grounded and activated by supply voltage.
Fig 5, Peak and frequency modulated hold, used on some GM throttle body systems. Figs 6, 7,and 8 display the injector current and voltage traces.
Helpful hint: Dynamic testing with a milliamp current probe is faster and more accurate than static testing with an ohmmeter. Use Ohm's law to determine the proper current level. Adjust the values for the number of injectors that are sharing each control circuit.
