Auto Service Professional

OCT 2018

Magazine for the auto service professional

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20 A S P O c t o b e r 2 018 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 sistance measured 145 ohms, thus causing a lean density misfire. Another example of a lean density condition can be seen in Figure 7 from a GM V6 4.3L Vortec engine. In this raster pattern notice the spark line duration, angle and presence of turbulence dur- ing a light power brake condition. is is another example how lean density conditions caused by bad or restricted injectors can be detected by reading a secondary ignition waveform. We have shown two examples of lean density misfires being detected by scope-checking the secondary ignition and focusing on the spark line during light load power brake conditions. We now want to show how a rich density condi- tion will show up on a secondary ignition wave- form. Notice Figure 8. We have used the super imposed screen of our scope. All cylinder firing events are stacked on top of one another. Notice that two cylinders' firing events show an elevated spark KV point. is occurs from the carbon fouled spark plug elec- trodes. In addition, notice the sloping downward spark line voltage from a rich condition. Remem- ber, fuel molecules are conductive, thus drasti- cally reducing the spark line voltage indicated by the sloping down spark line. In Figure 9 we have Figure 9: 2001 Dodge Caravan 3.8L (secondary super-imposed less #1 and #5) Here we have taken cylinders 1 and 5 off the screen. Notice that the other 4 cylinders have normal spark KV points and normal spark lines. Figure 10: Chrysler COP (primary/secondary) The Ford PCMs will multi-fire the coils below 1,000 rpms.

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