Home Diagnosis and TroubleshootingElectrical System and Electronics Bad Ignition Coil Symptoms – What Are The Symptoms?

Bad Ignition Coil Symptoms – What Are The Symptoms?

by Jordan Harris
Bad Ignition Coil Symptoms

Are you experiencing some misfires and weird engine work? You might be experiencing some bad ignition coil symptoms in your car. And if this is the case, then you are at the right place because we are going to cover everything you need to know when it comes to ignition coils.

Having a problem like this can be really frustrating because the engine works very strangely and develops symptoms like crazy. So, diagnosing it can be a tricky thing to do, and to be able to tell if one of the coils is bad you need to know all the possible symptoms connected to this problem.

That’s why you need to learn how to troubleshoot if you want to uncover problems like this. And troubleshooting is a true mastery that needs a lot of learning and wrenching to be achieved. But you shouldn’t worry because we are going to help you out with your trouble and teach you everything you need to know. That’s why we are here, we don’t want people to scratch their heads for a simple problem like this.

Because of this, in this article, we are going to learn everything when it comes to ignition coils. First, we will learn what coils are and how do they work. Then we will learn the bad ignition coil symptoms and how to diagnose this problem. Later we are going to cover the costs for the problem to be solved and how you can do it. If you want to learn more, follow along till the end.

What Are Ignition Coils?

Now before we dive into the bad ignition coil symptoms we need to understand some stuff and that is what are ignition coils in the first place? Not all of us are car-educated and there are people that need to catch up a bit. If you are more experienced you can jump right to the symptoms. If not keep up with us. So, what are ignition coils? Let’s elaborate.

Ignition coils are also known as electrical transformers. Remember back in the day when cars had wires from the distributor cap to the spark plugs? Well, these wires were replaced by these ignition coils and made the engine quite more compact than it was before.

Ignition coils have also improved the ignition overall and we can see fewer instances of modern cars that fail to start as we did back in the day when the distributor tends to fail and the wires as well and they had to be frequently replaced and all that. But not anymore.

This doesn’t mean that these coils are not failing though. They do but more rarely than before. Nevertheless, there is a single coil on each of the cylinders. This coil is transforming the 12V current into a much higher voltage and allows the car to crank and start. Then you can drive off and go to work or go to dinner. You can do everything when your car starts. But sadly sometimes it doesn’t.

And here the bad ignition coil symptoms come into play. But more on that, we are going to elaborate later in the article. Now let’s see why these coils are of such big importance and are quite essential for the car to run right.

Why Are Ignition Coils So Important?

Before we dive into the bad ignition coil symptoms let’s elaborate a bit on the importance of these ignition coils on the engine (it helps to learn how to test ignition coil).

As we know, they are really important because they are acting as transformers. They transform the power and deliver a proper current to each of the cylinders all of the time.

To put things into perspective, everything needs to work like clockwork so you don’t experience bad ignition coil symptoms. The electric current has to be delivered to the spark plugs equally across the whole engine.

An ideal spark will cause the gasoline to burn equally and proper explosions to be created into the cylinder. If the spark is weak or non-existent, there could be some problems with this engine and these problems will be present as bad ignition coil symptoms that we are going to elaborate on later.

Bad Ignition Coil Symptoms

Knowing this stuff, we can conclude that the coils are really essential and needed for the engine to work right. If you remove one coil, the engine will not even want to crank.

Modern engines are computerized. So, if the engine ECU detects that there is no coil in one of the cylinders the engine will not crank. Only a click-click sound will be heard. Technically a V8 could work with one cylinder down. But the computer simply will not allow this to happen. It will immediately throw bad ignition coil symptoms. More on that later. Let’s see first how these coil work under the hood.

How Do Ignition Coils Work?

So, before we cover the bad ignition coil symptoms, let’s learn how the ignition coils work in reality. This will be quite useful for the ones who want to get techier and want to understand how a component works in reality.

The ignition coil in reality is a transformer of electric current. As we noted, they are amplifying the 12V power that the battery is producing to an incredible power output that will blast the cylinders with enough electricity to start the vehicle’s engine.

They are electronic devices that are composed of two wire coils. These wire coils are then wrapped around a metallic core. The coils are marked as primary and secondary coils.

When the engine coil is blasted with electricity from the car battery, this electricity goes into the primary coil. But is disrupted by the secondary coil that is creating a strong electromagnetic field that later is charging the secondary coil with very high voltages. Much higher than the original 12V.

Then here comes the car computer into play. The car computer is regulating all of this process since it is connected with the coils directly. The computer is basically telling the coil when and how much electricity to transfer to the spark plug.

Isn’t this genius? Ignition coils have completely changed the car industry and made cars a lot more reliable. Not that engine coils cannot break and produce bad ignition coil symptoms. And more on this process, we are going to cover in the following chapters where we will elaborate these symptoms in detail.

Bad Ignition Coil Symptoms

So, as you know, every component when it brakes starts to develop symptoms. The engine coils also tend to produce bad ignition coil symptoms that could be quite an annoying thing.

Bad Ignition Coil Symptoms

A bad engine coil could sometimes make the use of the car unbearable and make you pissed off. When you experience bad ignition coil symptoms the engine simply works so weird and is quite an easy thing to diagnose these problems because of these symptoms that we are going to cover now. So, if you want to learn how to diagnose this problem follow along.

1. Check Engine Light

The check engine light would probably be one of the first bad ignition coil symptoms that you will encounter when you are dealing with this problem. Why is this the case?

This is the case because the coils are all connected to the ECU and the ECU is gathering the information of their work. If they fail to deliver then the ECU gets warnings and if there are too many warnings it will decide to show the check engine light on the cluster.

But beware, even if a coil is faulty the check engine light could not turn on. So, you can take this with a grain of salt. In 99% of the cases, it will show the check engine light message but there is still that 1% that could make to scratch your head.

So, a deeper diagnosing in some cases has to be done, and based on the bad ignition coil symptom a decision is to be made of what is causing this problem. Now, let’s move to the next symptom.

2. Engine Misfires

Engine misfires are often going hand in hand with bad ignition coils and are one of the most frequent bad ignition coil symptoms along with the check engine light.

Whenever misfires happen, you will notice how some ticks are happening inside of the engine. These are uneven explosions inside of the cylinder caused by bad ignition coils that cannot transfer enough power to the spark plug. The engine would be unhappy with this type of work and this could be also noticed on the exhaust.

There would be some pops coming from the rear. In more serious cases, there are backfires and a lot of smoke when this problem gets too serious.

Not an ideal situation, but a clear indication of bad ignition coil symptoms in my opinion. These misfires could be really annoying. But whenever you have misfires could also be because of bad spark plugs as well. So, checking the spark plugs first is quite essential to determine what is causing this problem. Now let’s move on to the other bad ignition coil symptoms.

3. Rough Idle

When we discuss the bad ignition coil symptoms we cannot avoid the rough idle. Whenever there are misfires, check engine light, and backfiring a rough idle will also be present.

This symptom can be manifested through increased vibrations inside of the cabin, most notably on the shift lever and the steering wheel. The engine will not be happy with this problem and will run rough.

Not to mention that the needle on the tachometer will show some weird symptoms, it will shake and the revs will often vary from 600 and up to 1200 or even more in some cases. A clear example of poor transformer work. This is one of the clearest bad ignition coil symptoms that could not be ignored. The important thing is to take things further and diagnose the problem.

Later in this article, after we cover the bad ignition coil symptoms we are going to cover the diagnosing process of this problem in detail and find out how this problem is sorted out in a speedy manner. Now let’s continue with the symptoms.

4. Engine Down On Power

Another in the list of bad ignition coil symptoms is the engine being down on power. If one or more coils are affected, the engine would be considerably down on power output. But why is this the case?

This is the case because in the cylinders there are no proper explosions. Whenever there is not a bang, there is no power produced. This makes the work of the other cylinders more challenging and is stressing them out to work harder in order for the engine to keep up.

Bad Ignition Coil Symptoms

Whenever you notice how the car is not happy and doesn’t perform as it did in the past. It is very important for you to diagnose the problem. This problem worsens the engine life and stresses out other components. Especially in smaller displacement engines that need every bit of spark to keep up running. Enough of this symptom now let’s move on to the following bad ignition coil symptoms.

5. Stalling Problem

Another in the list of bad ignition coil symptoms is the one when the engine simply loves to stall. The engine probably has a coil that is completely failed and the engine doesn’t have the ability to keep up working unless you press harder on the gas pedal and tell the engine to dump more fuel into the cylinders.

You will notice this problem mostly on idle when the engine RPMs simply drop below 800 and it sounds like the engine will shut down. In this situation, the only alternative for you is to press on the gas harder to make sure that the engine doesn’t shut off.

What is worse is that you will have to do this constantly and the engine will not like to run during idle without some feedback from you. This is a clear indicator that you need to take things further investigate the problem. Now let’s move to the last one of the bad ignition coil symptoms.

6. Poor Fuel Economy

And the last in our list of bad ignition coil symptoms that we are going to cover is the poor fuel economy. This symptom is closely related to the one that we covered above. Namely, the stalling issue.

Fuel economy consumption MPGs

So, how this happens is simple to explain, the engine tries to stall, you will need to make an adjustment to it. This adjustment often means pressing on the gas pedal and the more you press on the gas pedal, the more fuel is dumped into the cylinder. The more fuel is burned, the worse the fuel economy it is. Overall that is the situation and here we finish our list of bad ignition coil symptoms.

Reasons Why Bad Ignition Coil Symptoms Exist

Now after we have covered the bad ignition coil symptoms. Let’s discuss the reasons why ignition coils fail in the first place. This is very useful to know since you will probably know the cause for this problem that is happening to you.

The first reason why ignition coils fail is because of age. Age is a great factor when it comes to electrical components and the more the components age, the less chance you will have to run them in proper condition. Meaning that no matter how much these coils were used, they could still fail when they reach 15 years or so. So, when you want to do a major tune-up (to learn more, check out our guide on what is a tune-up on a car) of an older car, the best is to replace all of them at once.

The second reason why a coil could fail is overall use. As you know electrical components are used a lot and they transfer power all of the time while the engine is working. Meaning that they are under a lot of stress. So, use and abuse can affect their lifespan as well.

How To Diagnose & Replace A Bad Ignition Coil?

We have covered the bad ignition coil symptoms, now let’s learn how to diagnose the problem of bad ignition coils. How you can do this work at home?

The answer is simple, you only need to have an OBD2 scanner tool. With this tool, you will be able to scan the car for codes and if there are any, they will be reported to you and you will be able to check them out.

On basic code readers, you will only get the codes and you will later need to google them out and based on this information to determine.

Luckily there are more advanced code reader for car that work really well and tell you right away. The downside is that they are a bit more expensive.

Once you have this tool, you can scan the car for codes and see what the codes are showing. If they indicate a message of a misfire on a certain bank and cylinder. You need to inspect that specific coil and spark plug.

Then you can swap this coil for a different coil from another cylinder and scan the car for codes again. If the problem has moved to the other cylinder, then you know where to look for your problem. We have successfully diagnosed a problem with a bad coil based on the ignition coil symptoms and some common logic.

Now you can go to your local Autozone and purchase an ignition coil for your model. Then just plug the new coil into the engine and connect the connector. Pop the cover on and that’s it.

Now, you can go again and scan the car for codes and delete them if there are any. After this, the check engine light should be cleared.

Cost To Replace A Bad Ignition Coil

So, we learned the bad ignition coil symptoms and how to diagnose the matter. Now let’s see how much it is to replace the ignition coil?

On average, an engine coil costs about $150. It is relatively cheap and affordable. But if you do it by yourself. If you go to a shop they will charge you for diagnosing the matter and the labor and also the part involved in replacing this component.

So, when you add up everything, you can pay up to $300 for a single coil replacement. Shops are not cheap and for a problem like this, it is often advisable to have an OBD2 scanner tool and scan the car for codes whenever you want.

Coils are dead easy to diagnose and sort out. The important thing is that you have the desire to learn and everything can be sorted out. So, learn the bad ignition coil symptoms first and then learn how to diagnose and solve the problem.

Can I Keep Driving Like This?

So, what could happen if you decide to drive your car with bad ignition coil symptoms? Will the engine blow up? Well, actually no.

The thing is that these components are advised to be replaced but necessarily require replacing. If you want to drive a car like this with all these symptoms then you could do it.


But the reality is that nobody wants to have an underpowered car that often stalls and develops a ton of issues along the way. There is no satisfaction in that type of vehicle.

You need a good and reliable car that will last pretty much forever. In addition to the lack of comfort while driving. Your engine wear and tear would be more significant if you continue running this misfiring machine. You could reduce the engine life significantly. That’s why you need to learn the bad ignition coil symptoms and sort out this problem quickly.

Conclusion To Bad Ignition Coil Symptoms

In this article, we covered quite a bit when it comes to bad ignition coil symptoms. We learned what these coils are in general and what is their task. As we noted, they are acting as transformers that transform the 12V power from the battery into a much stronger current that then is blasted into the spark plugs.

Then we covered the bad ignition coil symptoms and as we saw, there are quite a few of them. Most notably the check engine light, engine misfires, and lack of engine power. Overall it is very easy to diagnose this problem and we covered that as well.

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