Oscilloscope Pattern #4

HFM-SFI

Primary individual pattern, 40 volt range.

Example of fault: defective spark plug connector.

1 Starting point of burn voltage line

2 Burn voltage line

3 Decay process

t Burn time

Primary ignition voltage in the 40 volt range at idle speed. Same problem as in Figure 3, but shown in the 40 volt range at engine idle speed.

The starting point (1) and the burn line is outside the 40 volt measuring range. The burn time of approx. 0.4-0.5 milliseconds is noticeably shorter. The decay process is normal.

Compared with the "normal" pattern (see Oscilloscope Pattern # 2), there is a distinct difference. Since two ignition sparks occur on the secondary side, it cannot be determined from the primary oscilloscope display which of the ignition coil's two high-voltage outputs has the defective spark plug connector.

Using a multimeter, check both ignition leads, including the spark plug connectors, of the ignition circuit that is indicated as faulty by the oscilloscope display.