Along with spark plugs and ignition cables, ignition coils play a vital role in a petrol engine’s ignition process. Used in the ignition systems of all petrol engines, the basic function of an ignition coil is to produce the necessary amount of high voltage needed so that a spark plug can ignite the fuel.
In general, there are two fundamental operating principles in ignition coil technology: ‘single spark technology’ and ‘dual spark technology’. With single spark technology, there is an individual coil for each spark plug supplied. With dual spark technology, one coil simultaneously ignites two spark plugs.
Through their design and the type of materials they are composed of, NGK SPARK PLUG produces reliable ignition coils that are heat and moisture-resistant in the engine bay, and that prevent oil and petrol vapours from harming the coil’s housing. In line with the company’s high quality standards, ignition coils guarantee reliable ignition, the highest level of electromagnetic tolerance and long durability.
NGK SPARK PLUG offers six different types of ignition coils. These are: Distributor Ignition Coils, Block Ignition Coils, Block Ignition Coils with two high voltage outputs, Pencil Coils with double spark and single spark technology and Coil Systems (also known as ‘rails’).
With a distributor ignition coil, the ignition coil generates a high-voltage pulse. This pulse passes through an ignition cable to a mechanical ignition distributor. After that, the high-voltage pulse is distributed to the corresponding ignition cable, which conducts the voltage to the cylinder. Older vehicles use this type of ignition coil. It was standard Original Equipment well into the 1990s.
A block ignition coil contains multiple ignition coils. These supply the spark plugs with the necessary high-voltage pulse through their respective individual high-voltage outputs and via ignition cables. Block ignition coils use single and dual spark technology.
This type of ignition coil performs the same function as regular Block Ignition Coils, with the exception that it has two high voltage outputs, meaning that one coil is able to create the required high voltage for two spark plugs. The use of block ignition coils with two high voltage outputs allows for half the number of coils to be used than normally would be. While this provides an obvious benefit, the spark plug does wear more quickly due to it being fired twice as often.
Pencil coils require no ignition cables; they are attached directly to the spark plug. As a result, the coil generates the high-voltage pulse directly at the spark plug. The advantage: there is essentially no voltage loss through the cable. In addition, this compact design leads to valuable additional room. This is particularly important in modern engines where space is at a premium.
This type of coil comes in two different forms, with either double spark or with single spark technology. The double spark coil features an additional output which fires a second cylinder via a cable, and is commonly known as ‘U4’. Whilst the reference ‘U5’ is a pure single spark coil with one coil per cylinder.
This ignition coil type comprises multiple ignition coils, which are combined to form a single, compact component. All ignition components are connected to the spark plugs in one step.
If a vehicle fails to start up, the engine misfires, there is a notable reduction in acceleration performance or the ‘check engine’ light simply turns on, the ignition coil(s) may be defective. Indeed, just like many other components, the ignition coil is also subject to a certain degree of wear and tear over time.
During the lifetime of a spark plug, the gap between the electrodes increases. This leads to a higher voltage needed to create a spark. This forces the ignition cable to work even harder to perform its role.
Pencil coils in particular can be subjected to extreme heat, which can then shorten the service life of an ignition coil.
Increased vibrations in the cylinder head may cause ignition coils (pencil coils in particular) to break.
The functioning condition of an ignition coil can be performed using an oscilloscope. It is recommended to have this action performed at a professional workshop.
The condition of a block ignition coil can also be tested by checking its electrical resistance with an ohmmeter. In this instance, the coil is removed before being tested, with the electrical resistance measured across the primary and secondary circuit. This is only possible if there is no diode or ignition module installed inside the ignition coil.
Correct installation is essential to enable the ignition coil to perform its work optimally over its entire service life. Excessive force, in particular, is to be avoided, with the vehicle application needing to be verified if the ignition coil does not fit.
The same applies to the plug terminals and ignition cables terminals, which must match the respective connections of the ignition coils. If an incorrect connection is used, the contacts will become oxidised and damaged.
The correct tools, moreover, should always be used, which is particularly important when there are specific service tools available. A good example of this is when pencil coils are fitted straight into the spark plug bores. These can be difficult to remove and are at risk of being damaged if a special extractor, enabling straight extraction, is not used.
Last but not least, all ignition coil attachment screws should be tightened to the correct torque.
In the more than a decade that NGK SPARK PLUG has been offering premium ignition coils, the range has consistently been expanded. The range has been further extended above 400 ignition coils covering 10,000 applications, now providing a pan-European car parc coverage of 92%. This development is set to continue with a further extension scheduled in the coming months.