Starter coil

Starter coil DEFAULT

What is a starter coil?

An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel.

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Then, what are the symptoms of a bad ignition coil?

Usually a faulty ignition coil will produce a few symptoms that alert the driver of a potential issue.

  • Engine misfires, rough idle, and loss of power. One of the most common symptoms associated with a faulty ignition coil is engine performance issues.
  • Check Engine Light comes on.
  • Car is not starting.

Similarly, can I replace just one ignition coil? You can replace one coil at a time or all at the same time. I would however recommend having all spark plugs replaced with the coils so you do not have to remove coils twice.

Also question is, what gives power to the ignition coil?

Power from the ignition coil is supplied to the rotor. The rotor spins in time with the engine. When the end of the rotor is near one of the contacts, electricity arcs to the contact. From there, the power travels down a spark plug wire to the associated spark plug.

Is it OK to drive with a bad ignition coil?

The answer is you should not. You can drive the car until it breaks down completely (and it will). While doing so you will, as pointed out by other answers, run the risk of damaging the converter but you also run the risk of fire. If the coil is faulty very bad things can happen.


Ignition Coil Problems, Symptoms and Solutions

There are several possible symptoms of an ignition coil problem. If your car is experiencing any of the problems listed below, you may have a faulty ignition coil on your hands: 

  • Engine misfires
  • Rough idle 
  • A decrease in car power, especially in acceleration
  • Poor fuel economy
  • Difficulty starting the engine 
  • Check engine light is on
  • Exhaust backfiring
  • Increased hydrocarbon emissions
  • The smell of gas coming from the exhaust 
  • Fuel leaks

What Is an Ignition Coil?

Before we take a closer look at any possible ignition coil problems, it will be useful to learn a little bit more about what an ignition coil is and how it works. 

The ignition coil, sometimes known as a spark coil, helps to start a car’s engine. It’s an essential part of the ignition system. 

A car’s battery has a low voltage (12 volts), but thousands of volts are needed to initiate the ignition on the spark plug. The ignition coil, which is basically a small transformer, transforms the 12 volts from the car battery into the thousands of volts needed. Without the energy provided by the ignition coil, the spark plug couldn’t create the spark that’s needed for combustion. Without combustion, your car isn’t going to start at all!

In this blog, we’ll be talking about a singular ignition coil, but most engines have at least four ignition coils, sometimes grouped together in a coil pack. If you have problems with your car’s ignition coils, it could affect your car’s performance. This is why it’s important to be alert for the symptoms of a faulty ignition coil, which we’ll run through in more detail now:

1. Difficulty Starting the Engine 

Difficulty starting your car’s engine could indicate a problem with your ignition coil. As explained above, most modern engines have multiple ignition coils. If you have several bad ignition coils, you could have a faulty ignition and difficulty starting your engine. Of course, there are a number of different problems that can make it difficult for an engine to start, so difficulty starting the engine alone isn’t enough to confirm an ignition coil problem. 

2. Engine Misfiring or Stalling

If your engine misfires or stalls when you are idle or when you stop suddenly or accelerate, there could be a problem with your ignition coil. A misfire — which can sound like a coughing or sputtering noise or feel like a jerk or strong vibration — means that one of the engine’s cylinders is not firing correctly. 

Misfires are more likely to occur when the engine is under strain, and they can generate emissions. This is why increased emissions and the smell of gas coming from the exhaust are symptoms of a bad ignition coil. As with difficulty starting the car’s engine, there are numerous other issues that can cause misfires that need to be ruled out before you can determine conclusively that the problem is with the ignition coil.

A faulty ignition coil can also cause the car to stall because of irregular sparks sent by the spark plug due to the faulty coil.

3. Poor Fuel Economy

If you notice that your car is getting less mileage from a full tank than usual, it could mean that you have a bad ignition coil. This happens because, when your spark plugs aren’t getting enough power (due to the faulty ignition coil), the system will try to compensate by injecting more fuel. This also means that fuel leaks can be a symptom of a bad ignition coil. 

Poor fuel economy can also be caused by a failing MAF sensor or a dirty engine filter, so these potential issues need to be ruled out as well. 

4. Check Engine Light

The check engine light is designed to tell you that there’s something wrong with the engine. If you’re driving with an ignition coil problem, your check engine light will pick this up and turn on. You should never ignore the check engine light, but as with the other symptoms we’ve discussed, the check engine light can be caused by a variety of different engine problems.

The easiest way to understand why an engine light is on is with an OBD-II (on-board diagnostics) check. A mechanic will be able to run an OBD-II check for you, or you can run your own OBD-II check using an OBD-II scanner. Codes P0300 to P0312 indicate misfires, while codes P0350 to P0362 are for ignition coil issues. 

Types of Ignition Coil

There are many different types of ignition coils that you should be aware of when trying to fix an ignition coil problem. For example, here are three different ignition coil types:

  • Coil-On-Plug (COP)
  • Coil-Near-Plug (CNP) 
  • Coil-Per-Cylinder (CPC)

The most common system, with multiple coils, is Coil-On-Plug (COP). There is one ignition coil per cylinder, with each coil connected to the spark plug. If there isn’t enough room for a COP, perhaps because the spark plugs protrude from the cylinder head, then you might have a CNP setup. In this case, the coils would be attached to the plug by short plug wires. 

Depending on whether you have a COP or CNP system, you’ll have to check for problems with your ignition coil in different ways, as we’ll detail in the next section. 

How to Test an Ignition Coil

Testing an ignition coil can be dangerous if done incorrectly. This blog is for informational purposes only. If you do not know how to safely test an ignition coil, you should get help from a qualified specialist. 

As noted in the “check engine light” section, you can check for ignition coil problems by running an OBD-II check, which will require an OBD-II scanner. Codes P0300 to P0312 indicate engine misfires, while codes P0350 to P0362 are for ignition coil issues. 

For most other kinds of ignition coil test, you’re going to have to take a look. The location of the ignition coil varies from vehicle to vehicle, so check your vehicle’s user manual or use a search engine to find where your car’s ignition coil is located. Again, take suitable precautions to make sure you don’t electrocute yourself. 

Once you’ve found your ignition coil, you can take a look for any obvious signs of damage. The easiest part is checking the ignition coil wiring. If any of the wires are damaged or deteriorated, this could be the source of your ignition coil problems. You should also take a look at the coil harness and connector for faults, especially bent terminal pins and loose connections. If you still can’t find a problem, you can remove each ignition coil from the engine and take a close look for signs of damage. Liquids can damage ignition coils, so pay close attention for signs of moisture. 

If you have a CNP ignition coil, there’s another test that you can run. You should always use insulated tools and wear thick rubber gloves for this kind of test.

  1. Turn off your car’s engine.
  2. Remove the spark plug wire.
  3. Attach a new spark plug to the spark plug wire.
  4. Using insulated tools, hold the spark plug’s threaded portion to some metal part of the engine.
  5. Using appropriate tools, remove the fuse from the fuel pump.
  6. Crank the engine. 

Once the engine is cranked, you should look for blue sparks along the spark plug gap. If you can see blue sparks, this proves your ignition coil is working correctly. If you don’t see blue sparks or you see orange sparks, this is a sign that there’s a problem with your ignition coil. When you’re finished, replace the parts to their previous positions. 

There are other tests you can run on your ignition coil depending on its type and your level of expertise. 

Ignition Coil Replacement Costs

If you’ve discovered a problem with your ignition coil, you can buy a replacement ignition coil online. Costs will vary according to your car’s make and model, but for older models, ignition coils will cost somewhere around the £50 mark. At YMF Car Parts, you can buy the Beckermann Ignition Coil 3Y36K, suitable for the 2013 Ford Fiesta, for £53.  

The good news is that an ignition coil problem is not an immediate safety concern, and it isn’t too expensive to repair either. You can even drive with a faulty ignition coil if you have to, though you’ll notice the car running poorly. Left unchecked, an ignition coil problem can damage other parts of the car, especially the catalytic converter, which could lead to larger problems if not dealt with.  

To find replacement car parts for your vehicle, simply enter your reg number, and our automated online system will do the rest. Also, get your Car Number plate fitting kits today. 

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Choosing Control Coil Size and Voltage for Motor Starters and Electrical Contactors

What is a Control Coil in Electrical Contactors and Motor Starters?

Control coils carry electrical current. The current is sent through the coilto generate an electromagnetic field. Control coils fail due to excess heat and vibration that can cause the insulating material to deteriorate. This puts stress on the control coil. Excess voltage also significantly reduces the electrical life of the coil.

Conditions reducing coil electrical life include:
  • Over voltage and high temperature
  • Physical obstruction preventing contactor from closing
  • Coil under voltage not producing enough force to keep the contactor engaged

What Size and Voltage Control Coil Do I need?

The Rated Coil Voltageis the voltage needed to power the motor starter or contactor. The correct rated voltage should be determined for standard operation.
To find this coil voltage for an electrical contactor, look on the contactor label, often on top, and usually near the screws on the front of the contactor. Once you find that number, you can refer to REPCO’s Control Coils for Starters and Contactorscatalog.

Stocking Wholesaler of Replacement Control Coils

Selecting the correct control coil for your motor starter and contactor is easy if you know the OEM number. Just go to the control coil catalogto find the correct size and voltage. You’ll see the REPCO equivalent to the OEM series and model number.
The catalog includes replacement control coils for major brands including: Allen Bradley; Cutler Hammer; GE; Siemens; Square D; Westinghouse. See a complete list of OEM replacement control coilsavailable.
Repco supplies replacement control coils and continues to build this line to complement Repco contact kits. Repco stocks replacements for many starters and motors that have been obsoleted by the manufacturer.

OEM Backorders Cost Time and More

REPCO is a NAED affiliate manufacturer specializing in replacement electrical contacts, carbon brushesand control coilsas a lower-cost option to OEM motor and control parts. Not only will you save money, you may also keep a customer or find new ones by cutting lead time.  A full line of electrical motor and control parts are available from stock. REPCO product specialists can be reached at 800-822-9190.
Starter solenoid Pull-in and Hold-in coils explained and tested

Ignition coil

Automobile fuel ignition system component

Aceon Bright Ignition Coil

An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car's 12-volt supply. The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads. Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser). More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. A modern passenger automobile may use one ignition coil for each engine cylinder (or pair of cylinders), eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses.

Ignition systems are not required for diesel engines which rely on compression to ignite the fuel/air mixture.

Basic principles[edit]

An ignition coil consists of a laminated iron core surrounded by two coils of copper wire. Unlike a power transformer, an ignition coil has an open magnetic circuit — the iron core does not form a closed loop around the windings. The energy that is stored in the magnetic field of the core is the energy that is transferred to the spark plug.

The primary winding has relatively few turns of heavy wire. The secondary winding consists of thousands of turns of smaller wire, insulated from the high voltage by enamel on the wires and layers of oiled paper insulation. The coil is usually inserted into a metal can or plastic case with insulated terminals for the high voltage and low voltage connections. When the contact breaker closes, it allows current from the battery to flow through the primary winding of the ignition coil. The current does not flow instantly because of the inductance of the coil. Current flowing in the coil produces a magnetic field in the core and in the air surrounding the core. The current must flow long enough to store enough energy in the field for the spark. Once the current has built up to its full level, the contact breaker opens. Since it has a capacitor connected across it, the primary winding and the capacitor form a tuned circuit, and as the stored energy oscillates between the inductor formed by the coil and the capacitor, the changing magnetic field in the core of the coil induces a much larger voltage in the secondary of the coil. More modern electronic ignition systems operate on exactly the same principle, but some rely on charging the capacitor to around 400 volts rather than charging the inductance of the coil. The timing of the opening of the contacts (or switching of the transistor) must be matched to the position of the piston in the cylinder so that the spark may be timed to ignite the air/fuel mixture to extract the most angular momentum possible. This is usually several degrees before the piston reaches top dead center. The contacts are driven off a shaft that is driven by the engine camshaft, or, if electronic ignition is used, a sensor on the engine shaft controls the timing of the pulses.

The amount of energy in the spark required to ignite the air-fuel mixture varies depending on the pressure and composition of the mixture, and on the speed of the engine. Under laboratory conditions as little as 1 millijoule is required in each spark, but practical coils must deliver much more energy than this to allow for higher pressure, rich or lean mixtures, losses in ignition wiring, and plug fouling and leakage. When gas velocity is high in the spark gap, the arc between the terminals is blown away from the terminals, making the arc longer and requiring more energy in each spark. Between 30 and 70 milli-joules are delivered in each spark.


Formerly, ignition coils were made with varnish and paper insulated high-voltage windings, inserted into a drawn-steel can and filled with oil or asphalt for insulation and moisture protection. Coils on modern automobiles are cast in filled epoxy resins which penetrate any voids within the winding.

A modern single-spark system has one coil per spark plug. To prevent premature sparking at the start of the primary pulse, a diode or secondary spark gap is installed in the coil to block the reverse pulse that would otherwise form.

In a coil meant for a wasted spark system, the secondary winding has two terminals isolated from the primary, and each terminal connects to a spark plug. With this system, no extra diode is needed since there would be no fuel-air mixture present at the inactive spark plug.[1]

In a low-inductance coil, fewer primary turns are used, so primary current is higher. This is not compatible with the capacity of mechanical breaker points, so solid-state switching is used.

Use in cars[edit]

Diagram of the Citroën 2CV wasted spark ignition system

Early gasoline (petrol) internal combustion engines used a magneto ignition system, since no battery was fitted to the vehicle; magnetos are still used in piston-engine aircraft to keep the engine running in the event of an electrical failure. The voltage produced by a magneto is dependent on the speed of the engine, making starting difficult. A battery-operated coil can provide a high-voltage spark even at low speeds, making starting easier.[2] When batteries became common in automobiles for cranking and lighting, the ignition coil system displaced magneto ignition.

In older vehicles, a single coil would serve all the spark plugs via the ignition distributor. Notable exceptions are the Saab 92, some Volkswagens, and the Wartburg 353 which have one ignition coil per cylinder. The flat twin cylinder 1948 Citroën 2CV used one double ended coil without a distributor, and just contact breakers, in a wasted spark system.

Modern ignition systems[edit]

Coil-pack of an Opel engine

Main article: Ignition system

In modern systems, the distributor is omitted and ignition is instead electronically controlled. Much smaller coils are used with one coil for each spark plug or one coil serving two spark plugs (for example two coils in a four-cylinder engine, or three coils in a six-cylinder engine). A large ignition coil puts out about 40 kV, and a small one such as from a lawn mower puts out about 15 kV. These coils may be remotely mounted or they may be placed on top of the spark plug, known as direct ignition (DI) or coil-on-plug. Where one coil serves two spark plugs (in two cylinders), it is through the wasted spark system. In this arrangement, the coil generates two sparks per cycle to both cylinders. The fuel in the cylinder that is nearing the end of its compression stroke is ignited, whereas the spark in its companion that is nearing the end of its exhaust stroke has no effect. The wasted spark system is more reliable than a single coil system with a distributor and less expensive than coil-on-plug.

Where coils are individually applied per cylinder, they may all be contained in a single molded block with multiple high-tension terminals. This is commonly called a coil-pack.

A bad coil pack may cause a misfire, bad fuel consumption or loss of power.

Related coils[edit]

See also[edit]


  • U.S. Patent 609,250, "Electrical Igniter for Gas Engines", Nikola Tesla, 1898.
  • U.S. Patent 1,391,256 - Induction coil structure - Arthur Atwater Kent - 1921
  • U.S. Patent 1,474,152 - Induction coil - Arthur Atwater Kent - 1923
  • U.S. Patent 1,474,597 - Induction coil - Arthur Atwater Kent - 1923
  • U.S. Patent 1,569,756 - Ignition coil - Arthur Atwater Kent - 1926
  • U.S. Patent 1,723,908 - Ignition system - Ernst Alexanderson - 1929


  1. ^Horst Bauer (ed)., Automotive Handbook 4th Edition, Robert Bosch GmBH, 1996, ISBN 0-8376-0333-1 pg.439-440
  2. ^V. A. W. Hillier, Hillier's Fundamentals of Automotive Electronics, Nelson Thornes, 1996 ISBN 0-7487-2695-0, page 167

External links[edit]

Look up ignition in Wiktionary, the free dictionary.

Coil starter

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How to Test Pull-in Coil \u0026 Hold-in Coil Motor Starters -- BGS Tutorial

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