The direct ignition (DIS) system is responsible for producing and controlling a high energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses one coil for each pair of cylinders. Each pair of cylinders that are at top dead center (TDC) at the same time are known as companion cylinders. The cylinder that is at TDC of the compression stroke is called the event cylinder. The cylinder that is at TDC of the exhaust stroke is called the waste cylinder. When the coil is triggered both companion cylinder spark plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance, the event cylinder uses most of the available voltage to produce a very high energy spark. This is known as waste spark ignition. The DIS system consists of the following components:

The crankshaft position (CKP) sensor is a permanent magnet generator known as a variable reluctance sensor. The CKP sensor produces an AC voltage of varying amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with a 58-tooth reluctor wheel attached to the crankshaft. As each reluctor wheel tooth rotates past the CKP sensor, the resulting change in the magnetic field creates an ON/OFF pulse 58 times per crankshaft revolution. The engine control module (ECM) processes the pulses to determine the crankshaft position. The ECM can synchronize the ignition timing, the fuel injector timing, and the spark knock control based on the CKP sensor and the camshaft position (CMP) sensor inputs. Using the CKP sensor signals in conjunction with the CMP sensor signals, the ECM determines the engine position with great accuracy. The CKP sensor is also used to detect misfire and for tachometer display. The ECM learns the variations between all 58 teeth under different speed and load conditions to correctly detect misfires. The CKP sensor circuits consist of a signal circuit, a low reference circuit, and a shielded ground circuit. Both CKP sensor circuits are protected from electromagnetic interference by the shielded ground circuit.

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 teeth and a reference gap. Each tooth on the reluctor wheel is spaced 6 degrees apart with a 12-degree space for the reference gap. The pulse from the reference gap is known as the sync pulse. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position, while the other teeth provide cylinder location during a revolution.

The camshaft position (CMP) sensor is a Hall-Effect type sensor. The CMP signal is a digital ON/OFF pulse, which outputs once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the engine control module (ECM) to determine the position of the valve train relative to the crankshaft position. By monitoring the CMP and crankshaft position (CKP) signals, the ECM can accurately trigger the fuel injectors. This allows the ECM to calculate true sequential fuel injection mode of operation. If the CMP signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. The CMP sensor consists of an ignition 1 voltage circuit, a ground circuit, and a signal circuit.

The camshaft reluctor wheel is bolted to the front of the camshaft. The wheel is a smooth track, half of which is of a lower profile than the other half. This track is read in a radial or axial fashion respectively. This allows the camshaft position (CMP) sensor to supply a signal as soon as the key is turned ON, since the CMP sensor reads the track profile, instead of a notch.

The ignition coil (IC) provides the voltage for 2 spark plugs simultaneously. The IC is a dual coil pack, and directly supplies voltage to each spark plug. The engine control module (ECM) will command the IC circuit ON, this allows the current to flow through the primary coil windings for the appropriate time or dwell. When the ECM commands the IC circuit OFF, this will interrupt current flow through the primary coil windings. The magnetic field created by the primary coil windings will collapse across the secondary coil windings, which induces a high voltage. The secondary coil voltage travels from the coil output terminal, through the spark plug wire, and across the spark plug gap to the engine block. The IC is not serviceable and must be replaced as an assembly. The IC consists of an ignition 1 voltage circuit, an IC 1 and 4 control circuit, and an IC 2 and 3 control circuit.

The engine control module (ECM) is responsible for maintaining proper spark and fuel injection timing for all driving conditions. The electronic spark timing (EST) is the method the ECM uses to control spark advance. The ignition module is integrated inside the ECM, and the primary coil ON/OFF is directly controlled by the ECM. To provide optimum driveability and emissions, the ECM monitors input signals from the following components in calculating ignition spark timing:

There is one normal mode of operation, with the spark under the engine control module (ECM) control. If the crankshaft position (CKP) sensor pulses are lost the engine will not run. The loss of the camshaft position (CMP) signal may result in a longer crank time since the ECM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.

The ignition coils secondary output voltage is more than 40,000 volts. Avoid body contact with the ignition high voltage secondary components when the engine is running or personal injury may result.

Be careful not to damage the secondary ignition coil boots when servicing the ignition system. Rotate each spark plug wire in order to loosen the boot from the spark plug before removing. Never pierce a secondary ignition boot for any testing purposes. Future ignition system problems are guaranteed if pinpoints or test lights are pushed through the secondary ignition component insulation during testing.