Integrated Electronic Ignition System: Description
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Integrated Electronic Ignition (EI) system consists of a Crankshaft Position (CKP) sensor, coil pack(s), wiring and PCM. Coil On Plug (COP) integrated EI system uses a separate coil for each spark plug and each coil is mounted directly onto spark plug. COP integrated EI system eliminates need for spark plug wires but does require input from Camshaft Position (CMP) sensor. The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.
- The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to crankshaft. The CMP sensor is used by COP Integrated EI System to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils. For additional CKP or CMP sensor information, see CAMSHAFT POSITION SENSOR or CRANKSHAFT POSITION SENSOR under INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
- The PCM uses CKP signal to calculate a spark target and then fires coil pack(s) to that target shown. See Fig 2. The PCM uses CMP sensor on COP Integrated EI Systems to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils.
- The coils and coil packs receive their signal from PCM to fire at a calculated spark target. Each coil within pack fires 2 spark plugs at the same time. The plugs are paired so that as one fires during compression stroke, the other fires during exhaust stroke. The next time the coil is fired, the situation is reversed. The COP system fires only one spark plug per coil and only on compression stroke. PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, battery positive voltage (B+) applied to coil primary circuit builds a magnetic field around primary coil. When the switch opens, power is interrupted and primary field collapses inducing high voltage in secondary coil windings and the spark plug is fired. A kickback voltage spike occurs when primary field collapses and the PCM uses this voltage spike to generate an Ignition Diagnostic Monitor (IDM) signal. IDM communicates information by pulse width modulation in PCM.
- The PCM processes CKP signal and uses it to drive tachometer as Clean Tach Output (CTO) signal.