Chart C-4F-2 Misfire Under Load

Chart C-4F-2:

Wiring Diagram:

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, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remaining high voltage to fire #1 spark plug.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.

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

1. If the "misfire" complaint exists at idle only, the diagnostic CHART C-4F-1 must be used.

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.

DIAGNOSTIC AIDS:

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