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DISTRIBUTORLESS IGNITION SYSTEM (DIS)
The DIS system, used on 4-cylinder engines, 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, which responds to 2 rotating metallic shutters mounted on crankshaft. One output from hall effect sensor, Profile Ignition Pick-Up (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 degrees) and low (zero volts) for other half of revolution.
The ECA determines Spark Output (SPOUT) by 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 fire. 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 random selection. Several attempts may be needed before DIS module selects proper coil, which will allow 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, which 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.
Monday, December 22nd, 2008 AT 8:40 PM