Chart C-4D-2 Ignition Misfire Under Load

Chart C-4D-2:

Chart C-4D-1 Wiring Diagram:

CIRCUIT DESCRIPTION

The direct ignition system (DIS) uses a waste spark method of distribution. In this type of 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 remainder of the high voltage to be used to fire #1 spark plug.

On this application, the crank sensor is mounted to the engine block and protrudes through the block to within approx. 050" of the crankshaft reluctor. Since the reluctor is a machined portion of the crankshaft and the crank sensor is mounted in a fixed position on the block, timing adjustments are not possible or necessary.


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

1. If the "Misfire" complaint exists at idle only, diagnostic chart C-4B-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 test gap on all leads. This simulates a "load" condition.

2. If the spark jumps the tester 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 tracing 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.

4. If the no 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.