Auto Service Professional

OCT 2018

Magazine for the auto service professional

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O c t o b e r 2 018 A SP 21 taken cylinders 1 and 5 off the screen. Notice that the other 4 cylinders have normal spark KV points and normal spark lines. On Ford and Chrysler COP-equipped en- gines, technicians can back probe the COP negative terminal and obtain a primary ignition waveform. e strategy here is that the spark line on a primary ignition waveform will mirror that of a secondary ignition waveform (see Figure 10). e Ford PCMs will multi-fire the coils below 1,000 rpms (see Figure 11). Above 1,000 rpm the PCM reverts to one firing event. Notice the 3 firing events from the primary side of the coil. e scope is set at .5 mil- liseconds per division. If we combine all three spark line duration periods we come up with about 1.5 milliseconds. Another unique ignition system can be found on some V6 Toyota engines. Figure 12 shows a combination COP/DIS system. e system uses an external igniter to control the coils. A coil is mounted directly on top of a spark plug, with a secondary lead going to the companion cylinder. is engine had a miss under road load condi- tions. is is a good example of the diagnostic power of accessing the primary side of the coil. First and foremost, notice the engine decal in Figure 13 indicating that dual ground electrode spark plugs are to be used. Now let's look at the primary waveform in Figure 14. Do you see a very short spark duration period? We removed a spark plug to find single ground electrode spark plugs were used. Aer replacing the spark plugs with the proper OE plugs, notice the good spark duration period in Figure 15. A GM 5.7L Silverado comes in with a type A misfire code (PO301). is is a coil near plug-type ignition system. Using the single cylinder selec- tion on our MT 5200 scope we clamped around #1 plug wire (see Figure 16). Notice the extremely low firing line voltage and the very long spark duration period. ese two factors told us the coil was not the cause. A compression test indi- cated 0 psi. Remember compression has a direct Figure 11: 5.4L COP primary multi-spark system Above 1,000 rpm the PCM reverts to one firing event. Notice the three firing events from the primary side of the coil. The scope is set at .5 milliseconds per division. If we combine all three spark line duration periods we come up with about 1.5 milliseconds.

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