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So, The primary ignition system consists of:
- The battery
- Ignition switch
- The resistor
- Ignition module
- Contact points
- Coil primary wiring
Consequently, The primary ignition system voltage is low; operating on the battery`s 12 volts. When the ignition is on, a low voltage current flows; from the battery through the primary windings of the coil. Then through the breaker points and back to the battery. As a result, This current flow causes a magnetic field to form around the coil.
So, How long the primary coil is turned ON is called Dwell. Once the maximum current is reached; the coil will be at its maximum power potential (strongest magnetic field). This is called coil saturation.
Consequently, Short Dwell times will not give enough time for the coil to become saturated causing a weak spark. In contrast, Dwell times that are too long will not increase the magnetic field. But, it will raise the temperature in the coil windings.
An ignition system must turn on the primary coil; long enough to reach maximum power. But, not so long as to overheat the coil. Modern systems use a power transistor to turn ON and OFF the primary coil windings. Consequently, This transistor is part of the Ignition Control Module.
Proper dwell and timing require sensors that monitor:
- Engine (RPM)
- Crankshaft and/or Camshaft Position
- Engine load
- Engine temperature
- And Include a Knock Sensor
So, Most engines use a Crankshaft Position Sensor (CKP) to monitor (RPM); and indicate which pistons are going up or down. Camshaft Position sensors (CMP) will indicate if the piston is on compression or exhaust. Consequently, It monitors engine (RPM). Manifold Absolute Pressure (MAP) sensors in combination with; Throttle Position sensors (TPS) will monitor engine load. However, most vehicles use Mass Airflow sensors (MAF) to monitor engine load.
When calculating spark timing, the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) will used as well. Finally, most systems use a Knock Sensor (KS). The knock sensor is a feedback sensor. So, Engine (RPM), Load and Temperature; are all used to calculate the Ignition timing. When timing is advanced the cylinder will knock or ping. When a ping or knock occurs the knock sensor signal; will retard the timing until the knock goes away.
Types Of Ignition Systems Include:
- Distributor Ignition System
- Direct Ignition System (DI)
- Coil-on-Plug (COP), Individual coil for each cylinder.
- Individual coil for each cylinder with separate HT (high tension) leads.
- DIS-Wasted Spark Ignition, separate coil for each two cylinders.
- Synchronous ignition with two secondary winding coil terminals.
Possible reasons for failure of the primary ignition circuit:
- No supply voltage to the ignition coil.
- Broken insulation between the coil’s primary and the secondary windings
- Bad ignition coil.
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