Auto Service Professional

OCT 2018

Magazine for the auto service professional

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24 A S P O c t o b e r 2 018 ery 100 millivolts = 1 amp. Some modern COP units have the igniter integrated into the coil so there is no access to the primary negative side of the coil should you consider accessing a primary voltage pattern. e PCM normally controls each individual igniter by forward biasing them with 5 volts which commands the igniter to turn on primary. When the PCM shis the 5 volts to 0 volts pri- mary is turned off and the coil fires. You already know that on some modern day COP-equipped engines the coils are buried with no accessibility. We simply need to read the schematic to deter- mine the color code of the B+ feed wire to the coils and clamp the amp probe around this wire at the easy access point. Notice the waveform in Figure 21 from a V6 Honda with a dead miss and no codes. Channel 2 is accessing the igniter con- trol signal from the PCM to the number 4 coil. Channel 1 is the amp probe clamped around the B+ feed wire to the coils and is set at 200 mil- livolts per division which converts to 2 amps per division. Notice that there is no primary event to the number 4 coil. What we do know is that the control signal from the PCM is there. is coil has the igniter integrated into the coil, which in this case turned out to be a bad coil/igniter. Notice the waveform in Figure 22 aer replacing the number 4 coil. In addition, the current probe can help us detect internal coil carbon tracking. Notice the coil amperage waveform in Figure 23. Aer the point of primary turn-off, notice the erratic transfer of energy from primary into secondary. is problem is very common in tak- ing out the primary drivers inside the PCM as in Ford and Chrysler systems. Some engine misfires are not caused by a problem in the secondary side of the coil or the I g n i t i o n W a v e f o r m D i a g n o s t i c s Figure 16: 2002 Silverado #1 cylinder secondary ignition Notice the extremely low firing line voltage and the very long spark duration period. These two factors told us the coil was not the cause on the GM 5.7l. Figure 17: 2002 Silverado #8 cylinder secondary ignition This shows a good secondary ignition waveform from a GM coil near plug system. Figure 14: Toyota 3.4L (bad primary) Do you see a very short spark duration period? We removed a spark plug to discover that single ground electrode spark plugs were installed. Figure 15: Toyota good primary After replacing the spark plugs with the proper OE plugs, notice the good spark duration period.

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