Chart C-4D-2 Misfire Under Load

Chart C-4D-2:

Wiring Diagram For EST:

CIRCUIT DESCRIPTION:

The Direct Ignition System (DIS) uses a waste spark method of distribution. With this type of system, the ignition module triggers a dual coil which results in two spark plugs firing at the same time. One cylinder is on the compression stroke and an opposite cylinder is on the exhaust stroke. This results in a lower energy requirement to fire the spark plug on the exhaust stroke, and the remainder of energy is used to fire the spark plug on the compression stroke. The crank sensor is mounted to the bottom of the coil/module assembly and protrudes through the block to within approximately .050 inch of the crankshaft reluctor. Since the reluctor is permanently attached to the crankshaft, and the crank sensor is mounted in a fixed position on the engine block, timing adjustments are not possible.


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

1. If the misfire complaint exists under idle only, see CHART C-4D-1. A spark tester, such as ST-125 or equivalent, must be used since it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plug. Spark should jump the test gap on all four leads. This simulates a LOAD condition.
2. If the spark jumps the test gap after grounding the opposite plug wire, excessive resistance in the plug bypassed is indicated. A faulty or poor connection at the plug could also result in a misfire condition. Check for carbon deposits inside the spark plug boot.
3. If carbon tracking is evident, replace the coil. Check the plug wires at the coil for being clean and tight. Excessive wire resistance or bad connections may damage the coil.
4. If the no spark condition follows the suspected coil, then the coil is faulty. Otherwise, the ignition module is the cause of no spark. Substituting a known good coil to perform the test may determine the no spark problem.