C-4D2 ~ Misfire Under Load

DIS Circuit:

C-4D-1 DIS Misfire Under Load Diagnostic Chart:

CIRCUIT DESCRIPTION:
The Direct Ignition System (DIS) uses a waste spark method of distribution. In this type of system, the ignition module triggers a dual coil, resulting in both connected spark plugs firing at the same time. One cylinder is on its compression stroke at the same time that the other is on the exhaust stroke, resulting in a lower energy requirement to fire the spark plug in the cylinder on its exhaust stroke. The leaves the remainder of the high voltage to be used to fire the spark plug which is in the cylinder on its compression stroke.

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

1. If the "Misfire" complaint exists at idle only, CHART C-4D-1 must be used. A spark tester such as at ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug. (25000 volts). Spark should pump the test gap on all 4 leads. This simulates a "load" condition.

2. If the spark jumps the test gap after grounding the opposite plug wire, it indicates excessive resistance in the plug which was bypassed. A faulty or poor connection at that plug could also result in the miss condition. Also check for carbon deposits inside the spark plug boot.

3. If carbon tracking is evident, replace coil and the sure plug wires relating to the coil are clean and tight. Excessive wire resistance or faulty connections could have caused the coil to be damaged.

4. If the spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition 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.