Free Delivery Over £30 Established in 1969 Click & Collect Available

Think you might have a bad ignition coil? In this blog, we run through the common ignition coil problems, symptoms and solutions so you can be sure your vehicle is working correctly.

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.