Chart C-4 Ignition Misfire Check

Chart C-4:

Fuel/Ignition Circuit:

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 and at the same time #4 cylinder is on the exhaust stroke, resulting in a lower energy requirement to fire the #4 spark plug. This leaves the remainder of the high voltage to be used to fire the #1 spark plug. On this application, the crank sensor is mounted to the engine block and protrudes through the block to within approximately .050 inch 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 engine block, timing adjustments are not possible or necessary.

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

1. The DIS uses two plugs and cables to complete the circuit of each coil. The other spark plug cable in the circuit must be left connected to create a spark. 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).

2. The test light should flash, indicating that the ECM is controlling the injectors. How bright the light flashes is not important.

3. Nominal resistance of each injector is 11.8 to 12.6 ohms at 20°C (68°F) (resistance will increase slightly at higher temperatures). All injectors should measure within 0.8 ohms of each other. Damage to the ECM injector driver may occur if any injector resistance measures less than 11.8 ohms (internal short to ignition CKT 439).

4. The spark plug cables should be measured with a ohmmeter for correct resistance (each wire should be less than 30000 ohms). This test will determine if the ECM is not triggering the coil module or if the Coil module is faulty.

5. Damage to the ECM injector driver may occur if injector driver CKT 467 or CKT 468 shorts to ignition CKT 439.