Chart C-4 Misfire Diagnosis

Chart C-4:

Ignition System Circuits:

CIRCUIT DESCRIPTION
The ignition system uses a waste spark method of spark distribution. In this type of ignition system the electronic 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.

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

1. Checks for voltage output of ignition system. The companion cylinder spark plug cable in the circuit must be connected to a good ground to create a good spark and avoid over stressing the coil. Test each spark plug cable with the engine idling (the ignition must be cycled "OFF" when moving the ST 125 tester to a different spark plug cable).

- Keep disconnected spark plug leads away from sensors and other electronic components.
- Move quickly through this test. Don't leave any spark plug lead disconnected for longer than 15 seconds.
- Let the engine run normally for 30 seconds between tests to avoid an excessive buildup of fuel.

2. If the spark tester fires on all wires, the ignition system, with the exception of the spark plugs, may be considered in good working order. If the spark plugs show no evidence of wear, damage or fouling, an engine mechanical fault should be suspected. Refer to Chart C-2A Fuel Injector Diagnosis. Chart C-2A Injector Coil Balance Test Procedure
3. Plug wires should be inspected for cuts or abrasions leading to shorts to ground or other components. This would cause a weak or absent spark yet the resistance valve when measured may be correct.
4. If carbon tracking is evident replace coil and be sure plug wires relating to that coil are clean and tight. Excessive wire resistance or faulty connections could have caused the coil to be damaged.
5. If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the electronic ignition control module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.