The main element responsible for the ignition of the air-fuel mixture in internal combustion engines is the ignition coil or transformer. With its help, high voltage is supplied to the spark plugs, which, of course, leads to the appearance of a spark. If the coil is damaged, the operation of the entire ignition system is disrupted, the engine can significantly reduce its power or completely stop working.

How does the ignition coil works?

The main task of the coil is to convert the low voltage supplied from the car battery, about 12 volts, to high voltage, up to 25.000-30.000 volts. In other words, the device of a typical ignition coil is actually an analog of a pulse boost transformer.

When you turn the ignition key, the mains close and low voltage is applied to the primary winding of the transformer. It has fewer turns and is made of thick wire. The passage of current through the primary winding causes the appearance of a magnetic field in which energy is accumulated.

When the primary circuit is interrupted (for example, by a mechanical chopper), the magnetic field creates a high voltage in the secondary winding. This, in turn, has a larger number of turns and is made of thin wire. Then a high voltage in the form of a pulse is supplied to the distributor, which separates it and supplies it to the electrodes of the spark plugs. A spark forms between the electrodes, igniting the air-fuel mixture.

Where is the ignition coil located?

The location of the ignition coil depends on its type and layout of the engine compartment. In modern cars, each spark plug has its own coil, the so-called individual. It is put directly on the spark plug and mounted on the valve cover of the engine. Common or double-output coils are usually located on the side of the top of the motor. The basic idea is to shorten the length of the high voltage wires.

Main features of an ignition coil

• Primary Inductance – The ability to store energy.
• Transformation coefficient – how many times the voltage supplied from the battery increases.
• Winding resistance. Each model has its range, so for a low voltage winding, the resistance can be 3-3.5 Ohms, and for a high winding it can be 5000-9000 Ohms.
• Spark formation energy.
• Breakdown voltage is the magnitude of the high voltage of the coil at which breakdown of the air gap occurs on the spark plug electrodes and a spark forms.

Types of ignition coils

The basic properties of induction coils are as follows:

• The inductance of the primary coating – the ability to store energy.
• Transformation coefficient – the number of times the voltage supplied by the car battery increases.
• Winding resistance. Each model has its own range, so for a low voltage winding, the resistance can be 3-3.5 Ohms, and for a high winding it can be 5000-9000 Ohms.
• Spark formation energy.
• Decomposition voltage – is the size of the high voltage of the coil at which there is a failure of the air gap on the spark plug electrodes and a spark is formed.

The most widely used are three types of designs:

• general,
• individual
• two-pin.

The simplest coils have two copper windings up to 150 rotations in the primary and up to 30,000 in the secondary. Both windings are insulated, which prevents a short circuit. The casing is a glass with a lid on which the contacts of the primary winding are brought out. The secondary winding is located inside the primary and is connected at one end to a low voltage winding.

The second end is also displayed on the lid of the coil and is designed to connect the circuit connecting the transformer to the spark plug. Inside the windings, there is an iron core that increases the strength of the magnetic field that is formed inside. Such types today are practically not used in the automotive industry. However, they can still be found in the repair of old cars and other vehicles.

The individual ignition coil is similar to the classical one and is used primarily in electronic systems. Structurally, it also has high and low voltage windings, but unlike the classical circuit, the primary is inside the secondary. Also, instead of one core, there are two – external and internal.

The first is inside the primary winding, and the second is around the secondary. The high voltage winding of individual ignition coils is equipped with a special diode. It cuts off high voltage currents. Individual coils are divided into two types that differ in the core design: compact and core.

The latter can be combined into modules of four. In one cycle, an individual coil forms one spark, which necessitates the synchronization of all coils relative to the engine camshaft.

Two-pin ignition coils

The design of a dual (two-pin) ignition coil is similar to the classical circuit, but the only difference is the presence of two terminals from the high voltage winding. This design allows you to form a spark simultaneously on two spark plugs. In the first of them, ignition occurs at the end of the compression stroke of the air-fuel mixture, and in the second – at the stage of exhaust emissions (idle).

Such designs are used in engines with an even number of cylinders. They allow to simplify the ignition system, and also to exclude the distributor from the circuit. Dual transformers are connected in two ways: both contacts are connected to the spark with high-voltage wiring; one contact is connected by a tip (directly with a spark plug), and the second by high-voltage wiring.

For four-cylinder engines, four-pin coils can be used, which are actually a system of a pair of two-pin coils.

Dry and oil-filled coils

In the classic ignition coil design, the interior is filled with oil. This is necessary so that under the influence of current its windings do not overheat. The body of such a coil itself is made of metal, which is not always rational. Therefore, in most modern cars an alternative design is used – a “dry” coil. It does not have housing but is covered with a layer of epoxy compound, which serves both as housing that protects against dirt and moisture, and a cooling system.

In addition, a number of imported cars use combined models combining a contact switch and a dry coil or involving the integration of a coil into a distributor.

How long do ignition coils last?

Theoretically, modern ignition coils have a lifespan of 60.000 – 80.000 kilometers (37.000 – 50.000 miles). However, actual performance is largely dependent on operating conditions. The causes of malfunctions can be many:

• Short circuit on the windings.
• Coil overheats.
• Depreciation as a result of prolonged use or increased vibration.
• Exceeding charging time. Most often this happens when the car’s battery does not provide the desired voltage level.
• Depressurization of the main components of the engine and fuel system.
• Damage to the housing.

Symptoms of a bad or failing ignition coils

Each spark plug has its own coil. The latter either connects to the spark plug using wires or is located above the spark plug. A spark of 15,000–20,000 V is required to form a spark on the spark plug electrodes. If the ignition coils are bad, misfires may occur which will lead to an increase in fuel consumption.

1. Check Engine light is on

Due to its essential role in the ignition system, the “check engine” light is expected to appear in the dashboard after a few driving cycles with a damaged ignition coil.

2. Increased fuel consumption

Without the necessary energy, the combustion process will not be efficient and there will be an obvious significant increase in fuel consumption. It should be noted that an increase in fuel consumption can also be caused by a faulty MAF sensor or dirty filters such as the fuel filter.

3. Difficulties while starting the engine

Depending on the number of faulty coils, you may experience difficulties in starting the engine. Rough engine start can also be caused by other problems with the electrical system, such as the battery, so it is preferable to eliminate these problems.

4. Possible engine errors

Due to the lack of energy required and due to the constant degradation, the ignition process will be affected, which in turn will affect the overall performance of the engine.

5. Engine stops during acceleration.

Engine power is directly proportional to the number of defective spark plugs. If the problem is very serious, you will feel a severe lack of power during acceleration. This can also be caused by problems with the injectors, so it is worth removing this option as well.

6. Hesitation of the engine during acceleration

Given the number of faulty coils, the engine will feel an acute lack of power, especially during acceleration. This can even be caused by various problems with the injectors and you will feel this best during acceleration. To eliminate the possibility of a problem with the injectors, it is preferable to analyze this variant as well.

7. Missfires

The fuel particles will not burn in the combustion chamber as they usually do and will enter the exhaust pipes with a high energy load. This energy will be unleashed in the form of mini-explosions.

8. High emissions

A faulty ignition coil will increase emissions, especially hydrocarbon emissions, which could be a problem for the environment, especially those living in an area that regularly checks for such problems.

9. Smell of gas in the exhaust pipe

Failure to burn the fuel in the combustion chamber will result in a spontaneous odor of gas coming from the exhaust pipe.

10. Unexpected stops

If the car stops while driving, this situation could be related to the ignition coil, although this could be very rare. Sometimes this happens when you are already stopped and other times it will happen as you move. If the coil starts to cool, it will send irregular currents to the spark plugs. You can also drive normally without any problems and then encounter problems later.

11. Loud noises

If you try to start the engine and hear a strange, repulsive noise repeatedly then you may experience an engine eruption that can be attributed to improper ignition coils. You can still drive the car, but you will hear a lot of strange noises and you will even feel stiffness when you accelerate.

How can you diagnose a bad or failing induction coil?

To perform such an operation you must have some basic knowledge of safety measures while working with a vehicle. Depending on the type of induction coils installed in your vehicle, you may need one or more of the following tools. A professional OBD II code scanner digital multimeter (DMM), car tester that gives you real-time data, ignition analyzers. Using these tools you can easily find out if the present symptoms betray a problem with the induction coil.

Using an OBD 2 code reader.

carefully analyze any error codes in the ECU using a professional car tester to help you find the information you need. For this step all you have to do is connect the code reader and turn on the ignition key (engine off).

Now that you know what codes have been stored in memory, you need to delete them. This is usually done by selecting the codes in the tool you are using.

Disconnect the OBD II code reader and start the engine, this condition is generally known as KOER (Key on Engine Running). If the warning lights on the car come on, stop the engine and continue diagnostics. If the test lights remain off, drive the vehicle for 5-10 minutes. If the lights remain off, you may have an intermittent problem. If the warning lights are on during the driving cycle, continue with the diagnostic process.

Visual inspection.

Perform a thorough visual inspection of the wires in each coil. Look for burned, damaged, or corroded wires. Pay special attention to any screws that are not in good condition or to open circuits caused by poor insulation.

It is now necessary to perform a thorough visual inspection of each coil connector. Make sure the ignition key is not open and disconnect each coil harness connector. Looking for all kinds of faults, weak connections, traces of corrosion or anything else can indicate a possible wrong connection.

To check the condition of the coils, each coil must be removed from the motor. Perform a meticulous visual inspection of each coil. Look for burned, damaged, or cracked coils. In addition, pay close attention to signs of water, oil, or moisture. Any liquid that comes in contact with the coil will damage it very quickly. It is preferable to resolve this situation as soon as possible.

Before proceeding with the next step, you need to resolve any issues that have arisen so far.

Electrical ignition coil tests

You need a digital multimeter (DMM) to perform this operation. Consult the corresponding wiring diagram and identify the terminal corresponding to the line. To measure the supply voltage, you will need to enter KOEO (Key on Engine Off) mode and rotate the digital multimeter in voltage test mode. After performing the measurement, if the value is less than 90% of the battery voltage, you need to check the entire line from the coil to the ECU.

Testing the ignition coil with a professional tool

A scanning tool that can give you real-time information is exactly what you need for this step. A car tester helps you diagnose faulty coils. Select the real-time data mode and search for the desired values. Ideally, no cylinder should report ignition problems. If a particular cylinder has a large number of gaps, you may suspect that this is caused by fuel injection, spark plug or induction coil as these are the most likely causes.

Some diagnostic tool manufacturers introduce special tests or functional tests for ignition coils. Follow the instructions given to you by the test tool to complete the operation.

Direct test

An ignition analyzer is required to perform these tests. Using an inductive ignition analyzer you can test the activity of the coil in real-time. Depending on the model of the tester, you can check the activation of the ignition coil, the approximate age, the output voltage of the coil and you can even get the graph of the ignition coil model.

The great advantage of this tool is that you only have to choose the coil you want to test. It is much easier to use inductive technology (the electric principle that drives ignition coils), so it is the most practical way to quickly and accurately test COP systems.

How can you replace a bad ignition coil?

You need a number of tools to perform this procedure. OBD II scanner, goggles, protective gloves, suitable screwdrivers, appropriate light using a flashlight.

• Make sure the ignition is off, and then disconnect the car’s battery. Detaching the negative terminal is usually sufficient.
• It is necessary to remove the coil connector. This step can be difficult for some models. Generally, the connector has a plastic strip that you need to push. But in many cases, there is a small safety clip that must first be removed with a suitable screwdriver
• Remove the coil. Most systems use a plastic cover to protect the coils. Lift the cover using the appropriate tool to remove the spool. Usually, the coils are attached with two screws.
• Install the new coil. Remove the old coil and then install the new coil. Double-check that you are using the part number.
• Reconnect the coil and battery. After completing the operation you can reconnect the coil with the safety clips and then the battery terminal.
• You are about to clear the DTC. Using the OBD II, clear the ECU to prevent the storage of any false codes. To do this you need to enter KOEO mode
• In the end, perform the driving cycle. When you have finished, drive for more than 10 minutes. Try to accelerate as you normally would.

Ignition coil replacement costs

The costs of new ignition coils are according to the car model. Some coils cost $70 while others cost $350. If you go to an automotive repair shop, expect to pay between $50 and $120 per hour of labor, even more, if you chose the dealership.