The image below shows a diagram looking at all factors which take place when the injector is actuated: This trace shows a voltage drop of approximately 100 milliVolts for a current flow of 800 milliAmps. When current flows within a circuit a voltage drop is created. This is the injector supply voltage, coupled to AC to clearly see the voltage drop. Point 3 displays the yellow trace on the waveform. This is more subtle than in the current trace, so testing multiple injectors on the same engine is recommended to remove ambiguity. Point 2 on the waveform shows a slight change in the voltage profile of the trace, which indicates that the pintle is now fully closed. OBD codes P020x will be stored if there is an anomaly with this induced voltage. The engine ECM uses the presence of this voltage to validate the electrical operation of the injector. This induces a Back EMF (Electro-Motive Force) into the winding and a voltage of 60 to 80 volts is observed. When the injector is to be switched off the ECM opens the path to ground and current flow ceases. The cursors on the trace indicate the injection duration, in this case 3.13 milliseconds. The current “ramps” up slowly due to the inductance (resistance) of the injector winding.Īt point 1 a change in the profile (knee point) of the trace will be observed, this is due to the pintle valve opening fully.Ībsence of this knee point is an indication that the injector either didn’t open or is stuck open i.e. Once the ECM completes the circuit this wire is “pulled” to ground, since a potential difference is now present across the injector winding current will begin to flow. When the injector is switched off, open circuit voltage (system voltage) is present on this wire, as the path to ground through the engine ECM is open.
The green trace shows the injector control circuit voltage.
#Fuel injector oscilloscope pattern software#
See how a Snap-on lab scope and diagnostic software can help you check voltage and amperage to guide you to a diagnosis when working on a faulty fuel injector.