Chart C-4D-1 Ignition Misfire at Idle

Chart C-4-1:

Ignition Circuit:

CIRCUIT DESCRIPTION:
The ignition system uses a waste spark method of spark distribution. In this type of ignition system the ignition 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. If the "misfire" complaint exists under load only, refer to Chart C-4D-2
Misfire Under Load Chart C-4D-2 Ignition Misfire Under Load Engine rpm should drop approximately equally on all cylinders.

2. A spark tester such as a ST-125 or equivalent must be used, because it is essential to verify adequate available secondary voltage at the spark plug. Secondary voltage of at least 25,000 volts must be present to jump the gap of a ST-125.

3. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.

4. By checking the secondary resistance, a coil with an open secondary may be located.

5. By installing a normally operating coil pack, a determination can be made as to fault being the coil or ignition control module.