Chart 3 of 4 - Ignition

Diagnostic Chart Part 3:

Schematic 3:

The PCM controls spark timing and dwell (spark On-time) under all engine running conditions. The electronic ignition (EI) module has the ability to charge and discharge each of the two coil packs independently based on PCM control. The PCM uses a high control signal of near 5 volts to charge up the coil and a low control signal of near 0 volts to discharge the coil. If the coil is charged and the control signal is low, the coil will fire through its secondary towers.

DIAGNOSTIC AIDS
A missing cam pulse to the PCM from the EI module via circuit 633 will NOT affect engine starting.

To determine if one of the two coils (1/4 or 2/3) is not firing, use Scan tool to monitor CALC. COMPRESSION OUTPUT while cranking engine.
^ If the 1/4 primary or secondary coil or 1/4 control circuit is inoperative, the Scan tool will display 000000110 or 00001100.
^ If the 2/3 primary or secondary coil or 2/3 control circuit is inoperative, the Scan tool will display 00001110 or 00000001.

The engine may or may not start on two cylinders.

Ignition voltage is supplied to the EI module and passed through the interconnect to the coils. If this circuit is open at the interconnect, neither coil will fire. ENGINE SPEED will indicate correctly, but CALC. COMPRESSION OUTPUT on Scan tool will remain at 00000000 when the engine is cranking.

Normal CALC. COMPRESSION OUTPUT with engine cranking or running should be 00000110 or 00001001 depending upon where the camshaft is.

IMPORTANT: If a bit in CALC. COMPRESSION OUTPUT is changing from a 1 to a 0 or vice versa while the engine is cranking, an ignition problem or compression problem is occurring. Refer to DTC P0300 for specific fault bit patterns. P0300

Primary ignition coil resistance: 0.41.6 ohms Secondary ignition coil resistance (tower 1 to tower 4 or tower 2 to tower 3): 3.8k-5.1k ohms