Auto Service Professional

FEB 2018

Magazine for the auto service professional

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13 | ASP February 2018 Technical spark plug air gap of the spark to overcome, (no more rotor air gap). Remember when a failure of the coil on the old distributor-equipped engine was rare, when one coil was responsible for firing all the spark plugs of a four-, six- or an eight-cylinder engine? Now that most modern day engines are equipped with COP-type ignition systems, a COP coil failure is becoming common. is begs the question — how does single coil and distributor-equipped engine reliabil- ity compare to common COP coil failures? If you are a technician who uses and appreciates the diag- nostic value of an amp probe coupled with a lab scope, most distributor-equipped engine coils required 4 to 6 amps for full coil saturation. As the rpm increased the point of primary turn on had to occur sooner to ensure enough charge time for sufficient coil saturation. Now with the new COP-type coils the PCM has sufficient time to individually control each individual coil's dwell period or coil saturation times. e benefit is that at higher rpm a weak spark from shortened dwell periods (such as those experienced on distributor-equipped single coil engines) has been pretty much eliminated. By comparison purposes, the new COP coils are now saturated with nearly double the amperage values with no limita- tions with reduced coil charge periods as rpm is increased, a common concern on single coil systems. ere are some distinct differences in the COP units now being used by the automobile manufacturers that can enhance our diag- nostic strategies when addressing a misfire. Ford and Chrysler COP units are directly controlled by the PCM, meaning the coil drivers are integrated into the PCM. e concern here is that shorted primary wind- ings or internal coil carbon tracking can take out the PCM. On the Ford COP-equipped engines, the PCM will multi fire the coils below 1,000 rpm to ensure good combustion during light load lean conditions (see Figure 3). Above 1,000 rpm the PCM will revert back to one firing event In addition, as we all know a pattern failure misfire on the Ford Triton engines is a loss of insulation on the secondary spark plug boot causing voltage to arc to the plug well. When- ever replacing spark plugs on these engines it is always highly recommended to replace the boots and suppressor springs. ese types of misfires usually occur under loaded accelera- tion conditions when the KV values increase as cylinder pressures increase. Also, I'm sure you have customers like mine who are waiting for the second coming to have their spark plugs replaced. On some modern Chrysler COP- equipped engines the PCM will monitor the collapse time of each individual firing time (spark duration), however, the actual values are not accurate and should be used for comparison between each individual coil firing times. You can get these values from your scan tool (see Figure 4). Good spark duration periods on COP-type ignition systems will vary between 1.5 and slightly over 2 milliseconds during a park warm idle no load condition. On Ford and Chrysler systems, using a lab scope and probing the coil negative termi- nal will yield a primary ignition waveform (see Figure 5). e primary and secondary waveform will mirror each other in the spark line area. e spark line characteristics we discussed earlier still apply. Notice, however, the secondary ignition waveform voltage per division is at 1 and 2 KV while the primary ignition waveform will vary between 10 and 20 volts per division. e scope time base is at 1 millisecond per division. Also, keep in mind that the scope's trigger level is best set just above the spark line voltage level. If the secondary KV demand is too high from, let's say, worn spark plugs or lean Figure 3

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