DISTRIBUTORLESS Ignition System (Dis)

The DIS system, used on 4-cylinder engine, is a dual plug system consisting of a crankshaft-mounted dual Hall Effect sensor, two 4-tower DIS coil packs and a DIS ignition module.

The DIS eliminates distributor by using multiple coils, each of which simultaneously fires 2 paired spark plugs. The first time a pair of spark plugs is fired, one fires during compression stroke and other during exhaust stroke. The next time same pair of spark plugs is fired, the roles are reversed. Although spark in exhaust stroke is wasted, little of coil's energy is lost.

Two ignition coils are mounted together in a coil pack. Since there are 2 plugs per cylinder, 2 coil packs are required. The right coil pack operates continuously whereas left coil pack may be switched on or off by ECA.

The ECA computes spark angle and dwell for ignition system. The crankshaft-mounted dual Hall Effect sensor is a dual digital output device responding to 2 rotating metallic shutters mounted on crankshaft. One output from Hall Effect sensor, Profile Ignition Pickup (PIP), is a 50 percent duty cycle signal, providing base spark timing information. The other output signal, Cylinder Identification (CID) signal, is required for DIS module to know which coil to fire. CID is high (battery voltage) for half of crankshaft revolution (180°) and low (zero volts) for other half revolution.

The ECA determines spark angle (SPOUT) using PIP signal to establish base timing. The SPOUT signal is produced and sent by ECA to DIS module and serves 2 purposes. The leading edge of signal fires coil and trailing edge of signal controls dwell "on" time. This feature is called Computer Controlled Dwell (CCD).

Another feature of system is Ignition Diagnostic Monitor (IDM). This is an output from DIS module to ECA which provides diagnostic information about ignition system for self-test.

Dual Plug Inhibit (DPI), another system feature, allows ECA processor to switch ignition system from single-to-dual plug operation. During cranking, vehicle is in single plug mode, only plugs on right side of engine are firing. When engine starts, ECA sends a command to DIS module to switch to dual plug operation.

If CID circuit fails, DIS module will randomly select one of 2 coils to fire. If hard starting results, turning key off and then cranking again will result in another guess. Several attempts may be needed until proper coil is selected, allowing vehicle to start and be driven until repairs can be made.

The Failure Mode Effects Management (FMEM) system will keep vehicle drivable in event of an EEC-IV system or ignition failure that would otherwise prevent spark angle or dwell commands. During FMEM, ECA opens SPOUT line and DIS module fires coils directly from PIP output. This results in a fixed spark angle of 10 degrees and a fixed dwell.