Description

IGNITION PRIMARY AND SECONDARY CIRCUIT

The ignition module is controlled by the ECM. This function is monitored by the ECM and faults are flagged as DTC 24. There are no diagnostic trouble codes for the remainder of the system: however, DTC 26 can be flagged if there is a severe ignition misfire, resulting in excess oxygen in the exhaust.

The ignition module switches the ignition coil primary circuit to ground. The coil saturation period (dwell) and peak coil current are also controlled by the ignition module. A function called "stall turnoff" prevents the coil overheating and battery discharge if the ignition is left ON without the engine running. The coil current is discharged slowly to avoid causing a spark.

The ignition secondary system uses a standard distributor rotor arm and cap. The distributor has no affect on ignition timing: it is simply a rotating switch for the secondary current.

Diagnostic Notes

1. The ignition secondary circuit can he monitored with a standard ignition oscilloscope.
2. The ignition module in 1990 MY XJ6 vehicles has 4 wires plus a ground; all later vehicles have 3 wire plus ground module. The 3-wire module can be used to replace the 4-wire module without modification.

Setting Distributor:

3. If misfiring occurs at high engine speed or load, check the distributor position in relation to the engine position. The distributor position is set using special tool JD 189 with the number 1 cylinder at TDC on the compression stroke.
4. A fault in the ignition system primary circuit will cause stalling or a "no start" condition. If there is no spark, use the diagnostic procedure shown.
5. A fault in the ignition system secondary circuit will usually cause an engine misfire. Use these examples of ignition secondary voltage oscilloscope patterns as a guide to diagnosing the problem.

Ignition Secondary Voltage Patterns

Ignition Secondary Voltage Patterns:

Circuit Diagram

Circuit Diagram: