Variances in this curvature between injectors can indicate a weak magnetic field and possible shorted injector winding. The CEMF adds "resistance" to the circuit and creates a voltage drop of its own. It is a result of the Counter Electromotive Force being created in the windings by the magnetic field that is building. See how the voltage trace curves slightly upward? As you'll see in a minute, this curve mimics the amperage pattern almost exactly. As the current flows through the injector windings, a magnetic field starts to build. Keep in mind that we are looking at something that for all practical purposes is happening instantaneously. If you find any, trace the cause as you would any other voltage drop. Compare the drop on each injector, and look for values outside the average.
![fuel injector oscilloscope pattern fuel injector oscilloscope pattern](https://1.bp.blogspot.com/-PatH9CkdNic/TqScokSnFlI/AAAAAAAAAPw/xbCqiSk76Qw/s1600/distriG-inj2.jpg)
Fuel injector oscilloscope pattern driver#
Depending on the type of driver used in the ECM, this drop can be as high as 0.70 to 0.80 volt. Where it stops above the "0" line is the amount of voltage drop in the circuit - something happening too fast to be measured with a DVOM. I first take a look at the end of the downward trace at the beginning of the pattern. I've reduced my voltage division to 0.10 volt, and my time division to 500 microseconds to zoom in on section B from Figure 3. Take a look at the highlighted area in Figure 6. I'm going to jump ahead a bit and show you all of this a little closer. You can see the voltage signal is pulled down to nearly 0.0 volt.but not quite. This is the start of the ECM's pulse width command.
![fuel injector oscilloscope pattern fuel injector oscilloscope pattern](http://3.bp.blogspot.com/_43jDKyabaZc/TKfvQ2_ubyI/AAAAAAAAARY/Jtgxu7-qDXo/s1600/injector+open+time.jpg)
The ECM has now completed the path to ground, energizing the injector. If not, take a closer look at the power side of the injector circuit up to and including the injector coil windings. This voltage should be within 0.50 volts of system voltage measured at the battery. Since the circuit is not closed at this time, there is no current flow and no voltage drop through the injector itself. In Figure 2, the highlighted section (A) is a measurement of system voltage to the injector and through the injector winding. Let's break this pattern into sections and take a closer look at what is going on in each. With the leads attached and the circuit running (engine idling), you should get a pattern similar to the one shown in Figure 1. Does this lead setup sound familiar? It should, as it's the same lead setup you would use in checking this circuit for voltage drop. The negative lead should attach to the battery negative post as close to the battery as possible.Īttach the positive lead to the groundside of the injector you want to test, as close to the injector as you can get. One advantage of the scope is the ability to adjust these two scales to take a closer look at any particular part of the pattern, and we'll do that as we go along. To set up your scope for viewing an injector pattern, set the time divisions (horizontal axis) at 2 milliseconds/division, and the voltage divisions (vertical axis) at 20 volts/division. It is also a good choice when monitoring a circuit that operates in milliseconds, like ignition systems or today's topic, fuel injectors.Ī DSO is nothing more than a voltmeter that graphs the voltage signal over time.
![fuel injector oscilloscope pattern fuel injector oscilloscope pattern](https://i.pinimg.com/originals/12/6d/ff/126dff7c91a9b388793e1c9abe6f8f6d.jpg)
It is excellent for checking electrical circuits for intermittent failures, voltage drops and even mechanical function. But there are still those occasions when I want to see what is happening directly without going through a "middle man," and those are the occasions I use my scope.Ī Digital Storage Oscilloscope (DSO) is a high-powered voltmeter that allows a user to monitor a voltage signal over time, viewing those results in a graph format on the viewing screen. More data parameters to use, faster refresh rates and better graphing all have played a role in making scan tool diagnostics easier. Modern scan tools, both OEM and aftermarket, have come a long way. Fuel Injectors fuel pumps fuel pump diagnosis fuel pump diagnostics digital storage oscilloscope DSOs using DSOs fuel systems repair shop repair shops automotive aftermarket Using a Digital Storage Oscilloscope to test fuel injectors adds depth to your fuel system diagnosis.