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Imagine a school hallway packed shoulder to shoulder with children running as fast as they can. This induced voltage frees electrons, offering resistance to the change in current flowing through the coil. As the field builds, it moves across the coil winding and in- duces voltage into the coil winding. As the magnetic field is building, the inductance offers resistance to the change in current flowing through the injector circuit. In other words, the larger the current, the larger the magnetic field. The magnetic field is proportional to the current and the number of turns in the coil. When current flows through a coil winding, all of the current is used to create a magnetic field around the winding (Fig. Photo: Karl Seyfert flow through the injector coil circuit. FUEL INJECTOR OSCILLOSCOPE PATTERN DRIVERIt dis- tor driver closed, current starts to Each part of the waveform (a34 January 2005 Once the PCM commands the injec- stand the electrical language. that can help you interpret and under- stand what’s actually occurring. However, an in- rent across the resistance of the PCM The oscilloscope is a powerful tool depth analysis is required to under- driver or gate (waveform segment C). produced by this injector looks like a remains in the circuit to push the cur- very simple signal. At first glance, the waveform The voltage drop is the voltage that have a story to tell. the internal components of this type of But when they’re linked together, they injector. 1 on page 36 illustrates voltage drop of. The cutaway across their output, causing a lower the electrical language. MOSFETs have less resistance changes are the letters or symbols of tion-style fuel injector. ![]() These belongs to the very common satura- output. This is due to In this electrical language, changes in The first waveform we’ll examine the resistance across the transistor’s voltage convey the information. If a transistor is used, the together to convey useful information. ![]() In a written language, letters join mation those waveforms provide. FUEL INJECTOR OSCILLOSCOPE PATTERN HOW TOThe initial volt- guage of the automobile is impulses, or like and explain how to diagnose age drop will depend on whether the changes in voltage (amplitude) over component faults based on the infor- electrical device used is a transistor or time. we’ll explain how certain vehicle elec- trical components work, show you The voltage should come very close The basic unit of the electrical lan- what their waveforms typically look to ground at this point. FUEL INJECTOR OSCILLOSCOPE PATTERN MANUALSA magnified view of tions, lacking a clear understanding of el that’s what instruction manuals the waveform can be seen in the low- the language spoken by the vehicles and training videos are for. This is what ertrain control module (PCM) driver many of us do every day when we at- Our purpose here is not to teach turns on, thus completing the injector tempt to diagnose vehicle malfunc- you how to use a specific scope mod- circuit to ground. waveform segment B when the pow- on that information. The voltage drops abruptly in making an informed decision based tion of the vehicle’s systems. Now, imagine being given contains unique information about the and there’s no current flowing at this the task of gathering information and electrical circuits that affect the opera- point. Each of these waveforms jector circuit has not been completed language. It’s referred to eign country and not information that’s needed to diagnose as open circuit voltage because the in- being able to speak the a vehicle. These electrical waveforms carry cuit or source voltage. This is the open cir- Imagine being in a for- form. that’s commonly referred to as a wave- ment A in Fig. Let’s look at waveform seg- happening around you. FUEL INJECTORWAVEFORMSSLICED EXTRA THIN BY BERNIE THOMPSONWe took a slice out of an injector to remind you that injector waveforms are nothingmore than snapshots of thin slices of time.L anguage is the key to plays voltage amplitude over time, record of voltage over time) has a sto- understanding what’s thus creating a visual display or graph ry to tell. ![]()
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