Ignition coil
Ignition coil: An ignition coil stores energy in its primary circuit and generates high secondary voltage when the magnetic field collapses. The page also includes a worked example and measurement sequence.
Technical frame
Ignition coil: An ignition coil stores energy in its primary circuit and generates high secondary voltage when the magnetic field collapses. The page also includes a worked example and measurement sequence.
The technical values here expose the standard, protocol or physical relationship directly; model-specific service values are linked through the matching model/variant dossier.
The goal is not only to define the term but to let the reader calculate and interpret what the data means in a scan, scope or physical test.
Concrete technical facts
- An ignition coil stores energy in its primary circuit and generates high secondary voltage when the magnetic field collapses.
- Primary stored energy is approximately E=½LI² from inductance and current squared.
- Dwell is the time allowed for primary current to build; too little can weaken spark while excessive dwell can overheat or hit current limiting.
- Current-ramp slope depends on coil inductance, supply voltage and primary resistance.
- Secondary firing voltage depends on plug gap, cylinder pressure, mixture and insulation, so there is no universal fixed kV target.
- Misfire diagnosis should separate coil command/current from injector operation and compression.
Worked example
- Example: with L=3 mH and 8 A primary current, ideal stored magnetic energy is E=½×0.003×8²≈0.096 J, or 96 mJ.
Measurement and verification sequence
- Record primary supply voltage and ECU trigger.
- Use a current clamp to observe dwell/current ramp and current limiting.
- Where safely accessible, compare secondary firing/burn behavior.
- Interpret coil-swap results together with injector and compression evidence.
Fault-separation logic
- Is a valid command present and are power/ground/network healthy?
- Does feedback follow the command?
- Does an independent physical measurement confirm the output?
- Is the fault limited to a specific temperature/load/speed condition?
- Does the result remain stable when the original condition is repeated after repair?
Technical sources
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