Chart C-4F Misfire

Chart C-4F:

Ignition & Fuel Injection Wiring Schematic:

CIRCUIT DESCRIPTION
The Electronic Ignition (EI) system uses a waste spark method of distribution. In this type of system, the electronic 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 remainder if the high voltage to be used to fire #1 spark plug. On this application, the low resolution 3X crankshaft position sensor is mounted to the engine reluctor is a machined portion of the crankshaft and the sensor is mounted in a fixed position on the block, timing adjustments are neither possible or necessary.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. "Current Weak Cylinder" on the Tech 1 will display the correct cylinder number only if a single cylinder is misfiring. If more than one cylinder is suspected of misfiring, disconnect the fuel injectors one at a time with the engine running and continue diagnosis on any cylinders which do not cause the RPM to drop when its injector is disconnected.
2. Ensures that the injectors are being actuated by the PCM. If not, the procedure in CHART A-3 (Page 1 of 2) should isolate the cause.Related Tests, Information and Procedures
3. A spark tester such as J 26792 (ST-125) or equivalent must be used to ensure adequate secondary voltage at the spark plug. Spark should jump the tester gap at all 6 leads. This test simulates a load condition.
4. If ignition coils are carbon tracked, the coil tower spark plug wire boots may be damaged.
5. By installing a normally operating coil, a determination can be made as to the fault being the coil or ignition control module.

DIAGNOSTIC AIDS
A misfire may occur intermittently or under extreme conditions. If a misfire cannot be duplicated, try spraying the coils and plug wires with a fine water mist to check for shorts.

A customer, under wide open throttle conditions, may experience fuel shut-off at high Rpm. RPM fuel shut-off point is PROM controlled, based on axle ratio. This could be interpreted as a misfire under load.