Chart C-4-2 Misfire Under Load

Ignition System Circuit Diagram (Type II):

Chart C-4-2, Misfire Under Load (Type II Ignition):

CIRCUIT DESCRIPTION:

The C3I 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 and vise/versa.

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

1. If the "misfire" complaint exists at idle only, refer to Chart C-4-1 Misfire Under LoadChart C-4-1 Misfire at Idle. If no weak cylinder is identified and all else checks out OK, Testing and Inspection
2. A spark tester such as a ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug (25,000 volts). Spark should jump the tester gap on all 6 leads. This simulates a "load" condition.
3. If ignition coils are carbon tracked, the coil towers, spark plug wires, or wire boots may be damaged.
4. By installing a normally operating coil, a determination can be made as to the fault being the coil or C3I module.

DIAGNOSTIC AIDS:

A customer, under wide open throttle conditions, may experience fuel shut-off at high rpm's. The rpm fuel shut-off point is MEM-CAL controlled based on axle ratio. This could be interpreted as misfire under load.