Chart C-4D-2 Ignition Misfire Under Load

Chart C-4-2:

Ignition Circuit:

CIRCUIT DESCRIPTION:
The ignition system uses a waste spark method of spark distribution. In this type of ignition system the ignition control module triggers the #1/4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1 cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remaining high voltage to fire #1 spark plug.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Simulates an engine load. Cranking the engine with the ST-125 installed on any plug wire should produce a crisp, blue spark. A cylinder that produces a spark significantly weaker than the others should be considered as having no spark.