Auto Service Professional

FEB 2018

Magazine for the auto service professional

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18 | ASP February 2018 Technical primary ignition voltage waveform is not possible. However, the amp probe becomes a valuable tool to ensure good coil saturation values. ese systems are unique in the fact that the PCM uses a separate IGT (ignitor trigger control circuit) for each individual coil. e PCM also monitors each coil's firing event by monitoring the IGF (ignition confirmation circuit). In the event of a loss of the IGF signal to the PCM, the PCM will shut down the cylinders injector. A loss of all of the IGF signals will cause the PCM to shut down all of the injectors. e scenario you could have here is that on a no start you could have no spark and no injector pulses at the same time. We have had a case where a Toyota came in as a no start indicating no spark and no injector pulses. Monitoring the IGF circuit with a lab scope showed no IGF pulses at all. As we unplugged number 3 coil the IGF pulses came back and the engine started — on 5 cylinders. e point here is that a bad coil can pull down the IGF circuit and cause the PCM to shut down all of the injectors and disable primary on the other cylinders. Figure 9 indicates a known good representation of the Toyota COP systems showing the comparison of coil amperage saturation, IGT (trigger) and IGF (ignition confirmation) from a single cylinder firing event. e bottom trace is the IGT signal while the middle trace is the IGF signal and the upper trace is coil current using the amp probe. Let's look at another example of an amp probe, not only looking at good coil saturation but also how well the energy is transferred between the primary side of the coil into the secondary side. Modern day ignition systems are known as "divorced," meaning there is no hard-wired circuit between the primary coil windings and the secondary coil windings. ere is simply an air gap. As the primary field collapses it is mutually inducted into the secondary windings across this air gap and multiplied several hundred times. Internal coil carbon tracking has a major effect on the smooth and complete transfer of this energy. Take a look at Figure 10. At the amperage waveform's point of primary turn off, note the erratic oscillations caused by internal coil carbon tracking. is problem can easily take out the primary coil driver in the PCM as in the Ford and Chrysler systems. We talked earlier about the use of a secondary lead between the coil and spark plug and then using our secondary KV probe around the plug wire to analyze more completely the firing and combustion event. Figure 11 shows a good secondary ignition Figure 7 Figure 8 Figure 9

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