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Ignition Coil

Ignition Coil


The ignition coil takes power from the battery and relays it to the spark plugs, which burns fuel, which makes your car run. If one or more of the ignition coils fail, your car's ability to run efficiently will be greatly hampered. The degree to which, and the number of ignition coils that are failing, as well as the total number of ignition coils the car runs on, determine the severity of the car's symptoms.


There are a variety of reasons an ignition coil may fail in a vehicle. An ignition coil is an integral part of every vehicle's ignition system that converts the car's alternator or battery voltage into enough power to create an arc within a spark plug. Newer vehicles may use one or more ignition coils; the car's onboard computer determines when the ignition coil should energize and distribute spark to the spark plugs. Older vehicles have a single coil and use a distributor that connects to the camshaft to distribute the ignition coil's spark to the spark plugs.

Fuel Economy


One of the first symptoms that a coil is no longer working as it should is a decline in your normal gas mileage. This is because it takes more fuel for the car to run when less power is reaching the spark plugs. So, when your ignition coil begins to fail and becomes less able to transfer power, your car requires more fuel to run, and your fuel economy suffers.




Also the result of increased, and less efficient, fuel use is a noticeable change in your exhaust. It may become black and smell of gasoline, rather than smelling like normal exhaust fumes.



One of the most common causes of ignition coil failure is overheating due to excessive spark gap. Spark plugs that are gapped excessively large require additional voltage for the spark to jump from electrode to electrode. This causes additional load on the ignition coils and subsequently causes the internal coils to heat up. During the excessive heating and cooling process, the coils expand and contract each time diminishing their integrity and causing malfunction or total failure.


Poor Connections


Many ignition coils require grounding; this may be achieved through mounting location or through an external wire. A loose or poorly mounted coil can cause problems with the ignition coil and may even result in permanent damage or failure. Loose spark plug wires can also cause the high voltage it produces to take the path of least resistance which is may be the nearest grounding point or the coil itself. If an ignition coil arcs across itself, then damage to the ignition coil may result.




If you do not catch the earliest symptoms of a failing ignition coil, your car may begin to experience serious backfires. This happens when unused fuel is emitted through the car's exhaust, creating a small explosion. Backfires can occur either in the car's manifold or in the exhaust pipe. Typically, backfires caused by ignition coil issues take place in the latter. If the problem is not corrected, these backfires can cause serious damage to your exhaust system, which will require costly repairs, which would otherwise be unnecessary.


Hard to Start


Because ignition coil failure means that a spark plug is no longer receiving an appropriate amount of charge, cars that are suffering from this issue are typically harder to start. This may be especially noticeable when the car is cold, or when the humidity level is high.




A series of misfires will often occur when ignition coils fail, resulting in your car running rough. When traveling at highway speeds, this may feel like a jerking sensation or a random, but repeated loss of power. At a stop light, or when idling for any reason, this feels like a vibration.




It is essential that your car continue receiving sparks to stay running. Cars that have ignition coil issues may stall, especially when idling, like at a stoplight or when left running while parked. This may become especially noticeable after the engine has been running a while and has "warmed up."



Failure to Start


A car whose ignition coil(s) completely fail will not start at all. In this case, jump starting will prove ineffective.


Diagnostic Symptom 

The most common way to mechanically diagnose a failing ignition coil is to check the wires that attach to the spark plugs for transfer of power. If, when tested, there is no "fire" in the wire, which would indicate no power was reaching the plugs, then your ignition coil is not appropriately converting and transferring energy from the battery to the spark plugs.

Primary coil: made of copper wire, which is thicker in comparison with that of the secondary coil. However, the coil itself is shorter than the secondary coil; to put it another way: It has fewer windings than the secondary coil 

Secondary coil: also made of copper wire, which is of a thinner consistency than that of the primary coil. An additional significant feature of this components is the number of windings, which is considerably greater in relation to the primary coil.

Diagram of the inside of an NGK cylinder ignition coil
Cross-section of a cylinder coil

In order to prevent electric discharge and spark-overs in the interior of the coil or outward, the wires of the primary and secondary coils must beinsulated.

This is satisfied by the quality of the winding on one hand, and the mould compound on the other hand.

A high-quality winding of the coil can be seen in the cross-section, whereby the wires are precisely arranged above one another, so that there is no recognisable spacing between them.

Mould compound: With all coils, except for the cylinder coils, an epoxy resin is used for this purpose - cylinder coils are normally filled with oil. By nature, the resin only liquefies at very high temperatures, therefore the potting of the ignition coil plays an especially important role in the production, because no air bubbles may form in the mould compound and the components are subjected to a very high thermal load.

Magnetic core: The magnetic core represents a key component of the ignition coil. It is laminated, which implies that it is usually comprised of several thin ferromagnetic sheets.
The primary purpose of the magnetic core is the formation of the magnetic field in the ignition coil, which is amplified as soon as voltage is applied. Energy is stored in the magnetic field. As long as the primary current is not switched off, the coil is referred to as being charged.

Diagram of an NGK cylinder ignition coil
Cross-section of a cylinder coil

High-voltage connection: Depending on the angle at which it is viewed, this connection is the end of the secondary coil or the connection point to the distributor and/or spark plug. Through this connection, the ignition voltage travels to the spark plugs, where a spark-over occurs.

With distributor and block coils, the ignition voltage travels over the ignition cables to the spark plugs. As the term distributor coil suggests, an additional distributor is required for this purpose. Pencil coils, on the other hand, sit directly on the spark plugs. An ignition cable is then only required when the ignition coil generates ignition energy for a second spark plug.

Terminals 1 and 15: Low-voltage connections/ minus(1)- and plus(15)terminals. The ignition coil is provided with current through these terminals.