System Diagnosis - Electronic Ignition

PRELIMINARY CHECKS:
Before attempting to diagnose the ignition system, a diagnostic circuit check should be performed.

Verify no diagnostic trouble codes are stored in malfunction history and that the diagnostic system is functioning properly.

Verify customer complaint.

Perform a visual inspection of:
^ PCM grounds for being clean and tight.
^ Wiring for proper connections, pinches and cuts. Also check for proper routing of wires.
^ Vacuum hoses for splits, kinks and proper connections and routing.


KNOCK SENSOR CIRCUIT
The knock censor circuit consists of a knock sensor, circuit 496 and the PCM. The sensor is mounted in the back of the engine near the top of the block and is used to detect abnormal vibration (spark knocking). Within the engine block, the sensor produces an A/C output voltage which increases with the severity of the knock. The PCM will retard timing to a maximum correction based on the signal it receives from the knock sensor.

The PCM will learn a minimum noise level at idle from the knock sensor and compare level at around 1500-3500 rpm. If the PCM sees no change in noise a DTC P0327 will set after an elapsed time. If the PCM cannot control knock whereas the sensor has detected too much noise due to an excessively noisy engine, a DTC P0326 will set.

The PCM will automatically retard spark to a value that corrected a knock problem previously if it exists again in that ignition cycle. The PCM however, will always try to work back to a zero compensation or no retard.

The knock sensor signal is only used during the TDC combustion event, which is determined by the 7x signal (knock window).


CRANKSHAFT POSITION SENSOR CIRCUIT
Crankshaft rotation initiates CKP pulses. With sensor connected to PCM, any valid CKP pulses will initiate reference pulses.

Crankshaft Position Sensor-Positive
The crankshaft position (CKP) sensor positive line is tied to the positive connection of the polarized variable reluctance crankshaft position sensor. The peak positive voltage depends on engine rpm, and ranges from 300 millivolts to 125 volts.

The CKP signal defines engine position. A CKP pulse occurs at each TDC, at 60 degrees after top dead center (ATDC), and at 120 degrees ATDC. A seventh pulse referred to as the sync pulse, occurs at 70 degrees ATDC of cylinder #1.

Crankshaft Position Sensor-Negative
The CKP negative line is tied to the negative connection of the polarized variable reluctance crankshaft position sensor. The peak negative voltage depends on engine rpm and ranges from -250 millivolts to -120 volts.


ENGINE STALL
If engine stalls, CKP pulses stop due to lack of engine rotation. Within 500 milliseconds after the last CKP pulse, any charged coils are fired. No more firing events will occur until engine rotation resumes. If an engine stall occurs where reference pulses are not received after the engine was running and the ignition volts indicate the ignition was not turned Off, an DTC P1599 will set.