What could be wrong with this secondary ignition pattern on this EI (DIS) vehicle? Two cylinders that are common to one coil are not firing. Is it an open circuit in the coil primary or secondary circuits? Is the ignition module failing to trigger the coil primary circuit?
Figure 1
A voltage drop test, with a lab scope, on the ignition module ground circuit can validate ignition module function and coil primary circuit integrity. Viewing the voltage drop on the scope screen shows the dwell period and discharge of each coil. Notice that every third signal is missing in Figure 2. This indicates that the coil primary could be open or the more probable possibility is that the ignition module has failed. Figure 3 shows a good signal.
Figure 2
Figure 3
