Oscilloscope Pattern #3

HFM-SFI

Primary individual pattern, 400 volt range.

Example of fault: defective spark plug connector.


1 Zener voltage

2 Starting point of burn voltage line

3 Burn voltage line

t Burn time

Primary ignition voltage in the 400 volt range at idle speed. One spark plug connector of one circuit is defective in this example (resistance approx. 1 megohm); there is some brief misfiring.

The Zener voltage (1) in this case is still approx. 340 volts, the starting point (2) is significantly higher at approx. 80 volts. The pattern (2) itself is distorted and the spark duration is shorter.