Diagnostic Notes

SYMPTOM DIAGNOSIS
An open or ground in the Ignition Control (IC) circuit will result in the engine continuing to run, but in a back-up ignition timing mode (base timing) at a calculated timing value and the Malfunction Indicator Lamp (MIL) "Service Engine Soon" will not be "ON."

The Powertrain Control Module (PCM) uses information from the Manifold Absolute Pressure (MAP) and Engine Coolant Temperature (ECT) sensors in addition to RPM to calculate spark advance as follows:

^ Low MAP output voltage = More spark advance.
^ Cold engine = More spark advance.
^ High MAP output voltage = Less spark advance.
^ Hot engine = Less spark advance.

Therefore, DETONATION could be caused by low MAP output or high resistance in the coolant sensor circuit.

POOR PERFORMANCE could be caused by high MAP output or low resistance in the coolant sensor circuit.

If the ENGINE CRANKS BUT WILL NOT RUN or immediately stalls, Chart A-3 must be used to determine if the failure is in the Electronic Ignition (El) system or the fuel system. Related Tests, Information and Procedures

IGNITION CONTROL (IC)
This system uses similar circuits between the Ignition Control Module (ICM) and the PCM that distributor type systems use. Following is a brief description of the IC circuit.

Ignition control A & B
The PCM sends the Ignition Control (IC) pulses to the 1CM on these circuits. These signals are similar to the 7X reference pulse square wave except that the PCM uses sensor inputs to determine the pulse timing to control spark advance.
When the PCM receives the 7X signal, it will determine which pair of cylinders will be fired (1 & 4 or 2 & 3).

DIAGNOSTIC TROUBLE CODE (DTC) 19
If DTC 19 is set, that chart must be used first for diagnosis. If the symptom is "Engine Misses" and the ignition system is suspected, use "Misfire" Chart C-4M for diagnosis. Chart C-4M Electronic Ignition System Misfire Diagnosis

TIMING
Because the reluctor wheel is an integral part of the crankshaft and the Crankshaft Position sensor is mounted in a fixed position, timing adjustment is not possible.