Chart 3

Diagnostic Chart (Part 3 Of 4):

Schematic:

IGNITION
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 the coil packs 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. During engine crank, the PCM will pulse the ignition control (IC) circuit 1 and 4 high and low to test for faults in IC circuit 1 and 4.

DIAGNOSTIC AIDS
If spark is present on any spark plug wire, the EI module power and ground circuits are OK.

A missing cam pulse to the PCM from the EI module via circuit 633 will NOT cause a no start.

If a coil is suspect, the Scan tool can be used to locate the condition. Monitoring MISFIRE CURRENT CYL. #1 and 4 or #2 and 3 can locate a coil if misfire counts are incrementing on mating cylinders 1-4 or 2-3.

The engine may or may not start on two cylinders.