Electronic Ignition System Description
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Electronic Ignition System Description
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Electronic Ignition System Operation
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The electronic ignition system produces and controls the high energy secondary spark. This spark ignites the compressed air/fuel mixture at precisely the correct time, providing optimal performance, fuel economy, and control of exhaust emissions. The engine control module (ECM) collects information from the crankshaft position sensor and camshaft position sensor - intake and camshaft position sensor - exhaust to determine the order, exhaust time, and spark plug timing for each of the cylinders. The ECM sends the frequency signal to the ignition coil assembly via the appropriate ignition control circuit so that the spark plug gets activated.
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Crankshaft Position Sensor
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The crankshaft position sensor circuits consist of an engine control module (ECM) supplied 5 V reference circuit, low reference circuit, and an output signal circuit. The crankshaft position sensor is an externally magnetically biased digital output integrated circuit sensing device. The sensor provides a pulse for each magnetic pole of the magnetic encoder wheel on the crankshaft. Each pole on the encoder wheel is spaced at 60-pole spacing, with 2 missing poles for the reference gap. The crankshaft position sensor produces an ON/OFF DC voltage of varying frequency, with 58 output pulses per crankshaft revolution. The frequency of the crankshaft position sensor output depends on the velocity of the crankshaft. The crankshaft position sensor sends a digital signal representing the crankshaft reluctor wheel to the ECM while the poles on the wheel spin past the crankshaft position sensor. The ECM uses each signal pulse from the crankshaft position sensor to determine the crankshaft speed, and decodes the reference gap on the crankshaft decoder wheel to determine the crankshaft position. This information is then used to determine the optimum ignition and injection points of the engine. The ECM uses output from the crankshaft position sensor to determine the camshaft position sensor - intake and camshaft position sensor - exhaust relative to the crankshaft, in order to regulate camshaft phasing and to identify when a cylinder is misfiring.
The crankshaft encoder wheel is part of the crankshaft. The encoder wheel consists of 58 poles and a reference gap. Each pole on the encoder wheel is spaced 6° apart with a 12° 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 poles provide cylinder location during a revolution.
The camshaft position sensor - intake and camshaft position sensor - exhaust is triggered by a notched reluctor wheel built onto the intake camshaft sprocket. The camshaft position sensor - intake and camshaft position sensor - exhaust provides four signal pulses to every camshaft revolution. Each notch, or feature of the reluctor wheel is of a different size which is used to identify the compression stroke of each cylinder and to enable sequential fuel injection. The camshaft position sensor - intake and camshaft position sensor - exhaust is connected to the ECM by the following circuits:
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A 5 V reference circuit
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The knock sensor system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation, also known as spark knock. The knock sensor system uses one or 2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the knock sensor detects. The control module receives the knock sensor signal through the signal circuit. The knock sensor ground is supplied by the control module through the low reference circuit.
The control module learns a minimum noise level, or background noise, at idle from the knock sensor and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal knock sensor signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal knock sensor signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses knock sensor signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel.
If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal signal from the knock sensor will lie outside of the noise channel or will not be included. The knock sensor diagnostics are calibrated to discover faults in the knock sensor control unit, the knock sensor's cable routing or the knock sensor's output signal. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.
The ignition coil assembly used on this engine integrates the 4 coils and the module within a single sealed component.
The ignition coil has the following circuits:
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An ignition voltage circuit
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4 ignition control (IC) circuits
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The ECM controls the individual coils by transmitting timing pulses on the electronic ignition circuit of each ignition coil to enable a spark event.
The spark plugs are connected to each coil by a short boot. The boot contains a spring that conducts the spark energy from the coil to the spark plug. The spark plug electrode is coated with platinum for long wear and higher efficiency.
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Engine Control Module (ECM)
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The ECM controls all of the ignition system functions, and constantly corrects the spark timing. The ECM monitors information from various sensor inputs that include the following:
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The crankshaft position sensor
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The accelerator position pedal (APP)
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The manifold absolute pressure (MAP) sensor
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The intake air temperature (IAT) sensor
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The vehicle speed sensor (VSS)
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The engine knock sensor
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The engine coolant temperature (ECT) sensor
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The mass airflow (MA) sensor
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The camshaft position sensors
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