![]() ![]() 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. Red channel: fuel injector current flow.Green channel: fuel injector control circuit.Yellow channel: fuel injector supply circuit.The waveform below was captured from a vehicle using the setup above: Optional – backprobe supply wire to monitor voltage drop, couple scope to AC and select 500 millivolt scale, position zero line at 350 millivolts.Backprobe control wire with suitable probe to monitor current flow.Arrow points in the direction of current flow (conventional current flow, positive to negative).Position clamp around either the supply or control wire.Switch on low amp clamp and zero to calibrate.Set channel 2 to 2 Amp scale, (Low amps 20), position zero line at 0.2 amps.Set channel 1 to 100 volt scale, (DC Volts), position 0 zero line at 5 volts.Below is an outline of the steps to setup the test: Mechanical movement of the pintle valve will be observed in the current and voltage traces on the waveform. The fuel outlet is now open and fuel will be delivered on to the back of the intake valve (s). This duration or period is referred to as the injector pulse width.Ī typical pulse width is 2 to 4 milliseconds at idle and as high as 15 to 18 milliseconds at wide open throttle.Ĭurrent flow through the winding will result in the creation of a large magnetic field, which has the effect of “attracting” the pintle valve into the winding. When the injector is to be actuated, the engine control module connects the negative side of the winding to ground through a transistor.Ĭurrent will flow through the injector winding until the path to ground is interrupted. ![]() In the diagram below the fuel injector is supplied with a hard live from a fuse. High pressure injectors fitted to direct injection spark ignition and common rail compression ignition engines use hydraulic imbalance to open the injector, so this test is not suitable for these applications. This test is only applicable to low pressure fuel injectors due to the construction and operation of the injector. The mechanical operation of a fuel injector on a spark ignition engine can be assessed with an oscilloscope using a two channel test. #FUEL INJECTOR OSCILLOSCOPE PATTERN SOFTWARE#When engine is old, single pattern of one cylinder shows there is a fault in the system, but if all cylinders are similar, this engine should be fine, maybe just worn and aging.Ĭyl 1: Firing Voltage = 6.4kv Burn Time =1.39msĬyl 2: Firing Voltage = 5.2kv Burn Time =1.32msĬyl 3: Firing Voltage = 6.2kv Burn Time =1.19msĬyl 4: Firing Voltage = 6.1kv Burn Time =1.45msĬyl 1: Firing Voltage = 9.8kv Burn Time =1.15msĬyl 2: Firing Voltage = 8.4kv Burn Time =0.84msĬyl 3: Firing Voltage = 9.9kv Burn Time =0.84msĬyl 4: Firing Voltage = 9.0kv Burn Time =1.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. Raster or stacked display can let us compare all cylinders. We need accurate testing to find out fault in the area. The pattern can help us to diagnosis the fault in the ignition system, but it just gives us the direction of the faulty area. Large spark plug gap or high resistance in the circuit may cause this problem. WS3 - Oscilloscope Patterns to CaptureThe reading is not normal. ![]()
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