Direct Ignition System (Dis)

CAUTION: Avoid running engine if there is a possibility of the secondary circuit becoming open. Ignition power stages and/or the ignition coils could be damaged through excessive energy being reflected back into the primary circuit.

Discovery & Range Rover

Ignition and spark distribution are controlled by DIS. DIS uses 2 quad-ended ignition coils located at the rear of the engine. ECM provides internal switching of ground circuit for each coil, which operate on a waste spark principle. A spark is delivered simultaneously to 2 cylinders, one on its compression stroke and the other on its exhaust stroke. Coil No. 1 feeds cylinders No. 1 and 6. Coil No. 2 feeds cylinders No. 5 and 8. Coil No. 3 feeds cylinders No. 4 and 7. Coil No. 4 feeds cylinders No. 2 and 3. Failure of any coil will cause a misfire in 2 cylinders.
Ignition timing is controlled primarily as a function of engine speed, temperature, load, knock and idle speed controls, and A/T shift control. Engine load is sensed by Mass Airflow (MAF) sensor. Engine speed is sensed by a Crankshaft Position (CKP) sensor. ECM determines correct firing sequence and timing of ignition coils from input provided by Camshaft Position (CMP) sensor. During engine warm-up, ignition timing is approximately 12 degrees BTDC. TestBook/T4 can not directly diagnose the high-tension side of the ignition system. Ignition related faults are monitored through the misfire detection system. An ignition coil fault is indicated by illumination of the MIL.

Freelander

The ECM uses a separate ignition coil for each spark plug. The ignition coils for the left (front) cylinder bank spark plugs are positioned on the forward tracts of the intake manifold and connected to the spark plugs with High Tension (HT) leads. The ignition coils for the right (rear) cylinder bank spark plugs are the plug top design, secured to the camshaft cover with 2 screws. Each ignition coil has 3 connections in addition to the spark plug connection. The 3 ignition coil connections are:
- Ignition feed from main relay.
- Ground wire for secondary winding.
- Primary winding negative (switch) terminal.
The switch terminal of each ignition coil is connected to a separate ECM pin to allow independent switching. The ignition coils are charged whenever the ECM supplies a ground path to the primary winding negative terminal. The duration of charge time is held relatively constant by the ECM for all engine speeds. Consequently, the dwell period increases with engine speed. This type of system, referred to as "constant energy", allows low impedance coils with faster charge times and higher outputs to be used. The ECM calculates dwell period using the following inputs:
- Battery voltage (main relay).
- CKP sensor.
- Ignition coil primary current (internal ECM connection).
Spark is produced when ECM breaks the primary winding circuit. This causes the magnetic flux around the primary winding to collapse, inducing high tension energy in the secondary coil, which can only pass to ground by bridging the spark plug air gap. Ignition related faults are monitored indirectly by misfire detection function.