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Ignition coil




The ignition coil's job is to store ignition energy while the primary circuit is closed and, once the primary circuit is opened, to release at least a large portion of it to a specific spark plug via the secondary circuit. The current aligns the dipoles (smallest magnetic units) in the soft iron of the ignition coil (animation above), thereby amplifying the magnetic field of the primary winding. The energy is induced in the secondary winding and flows away when the primary magnetic field collapses.


This is the economy circuit used in earlier versions of the ignition coil. The primary and secondary windings are connected to each other at one end and to terminal 1.


Here, the two circuits are completely separated from each other. Despite this galvanic isolation, when working on the ignition, one should never assume that high voltage cannot also arc over to the primary system. In today's dual-spark coils, a spark plug is connected to both 4a and 4b, whereas in single-spark coils, the spark plug is only connected to 4, and 4a is connected to ground.

Ignition coil faults should not only be corrected by replacement, but also verified through measurements. Once you're sure of the voltage supply and the presence of a signal at terminal 1 requesting ignition, you're likely to use an ohmmeter to measure both coils and possibly compare them with the manufacturer's specifications.

This is a net with relatively large meshes. It might be fine for fishing, but when it comes to ignition, it only detects genuine breaks in the coils. You can also measure the resistance of each coil against the housing, but this will only be successful if there is direct contact.

These aren't exactly typical ignition coil faults. For example, what kind of movement is possible within a potted system without it being perceptible from the outside? More likely is the influence of temperature, especially with single-spark coils, or the formation of small cracks through which a spark can strike ground.

In addition, with an older ignition coil in a power-saving circuit, the measurement may still be possible without problems, but later versions may have a diode in the secondary circuit, making it better to measure in both directions with the ohmmeter. The success of a measurement also depends on the forward voltage of this diode, which can be significantly higher than the familiar 0.7 V in the high-voltage section.

So if the ohmmeter doesn't detect continuity, don't immediately throw away the ignition coil. With 12V and a (diode) test lamp, it should work, or you've successfully isolated the defect. And if positive is present, you can usually still coax a spark from the coil by connecting the sole or respective terminal 1 to ground.





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