Home Uncategorized 10 Ignition Coil Symptoms That You Need to Take Seriously
ignition coil symptoms

10 Ignition Coil Symptoms That You Need to Take Seriously

by Martha Simmonds

The ignition coil lives in the shadow of spark plugs. Still, it does most of the heavy lifting in the ignition system. So, when it fails, it can negatively affect the performance of your vehicle. Knowing the critical bad ignition coil symptoms will help you prevent that.

The car has its ways to hint that something is wrong with the coil. You just need to learn to recognize the early warning signs.

Unfortunately, many drivers ignore these signs. That is because the car may still start even when the coil gives out. But there are ten bad ignition coil symptoms that you need to take seriously. Those are:

  1. Backfiring
  2. A gas smell coming from the exhaust
  3. Oil leaks
  4. Misfiring
  5. Engine stalling and rough idle
  6. Hesitation of the engine during acceleration
  7. Decreased fuel economy
  8. Increased emissions
  9. The car failing or struggling to start
  10. Check engine light going on

Before you make a diagnosis, you first need to get to know this “patient.” That will help you determine what causes each symptom. Only then will you find the right course of treatment.

What Is an Ignition Coil and How Does It Operate?

The ignition coil is a small electrical transformer. Its job is to pull voltage from the battery and send it to the spark plug.

Most cars use 12-volt batteries. In contrast, the spark plug needs at least 12,000–25,000 volts to provide a spark. So, the ignition coil transforms the battery’s low-voltage current to a high-voltage one.

That starts a chain reaction. The spark plug creates a spark that ignites the fuel. Once that happens, the car engine starts.

Building Components

A car’s ignition coil consists of an iron core and two circuits: primary and secondary. When the coil draws current from the battery, it goes into its primary winding. That process creates a magnetic field around the core.

The magnetic field falls apart when the current is cut off. The accumulated power is then sent to the secondary circuit. There, the voltage is amplified.

Decades ago, vehicles relied on one ignition coil. Today, car engines are more powerful. As a result, many ignition systems feature one coil per spark plug. They are called COP, or Coil-On-Plug.

Some automobiles have one coil per two cylinders. That’s a rare configuration, however, and this article will focus mainly on direct ignition systems (COP systems).

How to Find It?

It is useful to know how to locate the ignition coils in your car. For example, you may need to check if they are in good condition. Being able to find the coil will also help you diagnose different ignition problems.

Usually, the coils are on the right side of the engine. They are “hiding” under individual caps. You will spot them by the wire coming out from each of those caps. The spark plugs are under the ignition coils.

10 Ignition Coil Symptoms That You Need to Take Seriously

1.   Backfiring

Black smoke exiting the exhaust pipe is one of the first faulty ignition coil symptoms. It is also known as backfiring and it happens when there is fuel in the cylinders of the internal combustion engine.

Do not underestimate this issue. It may suggest that one or more of your coils are damaged. Furthermore, it can hurt the exhaust’s performance.

2.   A Gas Smell Coming From the Exhaust

Check your coils if you notice a gas smell coming out of your exhaust pipe. That is also a result of leftover fuel in the engine’s cylinders. You should be able to sense the smell even when the car is off.

3.   Oil Leaks

Have you found oil on the coils in your ignition system? That suggests that the coil housing is broken and has started to leak oil. Address this issue as soon as you can. Otherwise, the oil leak may reach the carburetor and damage the car.

4.   Misfiring

The ignition coil has two windings. They help it convert high voltage for the spark plug. If one of these windings stops workings, the spark plug cylinder won’t ignite. That leads to misfires.

5.   Engine Stalling and Rough Idle

There are different signs that your engine is misfiring. Engine stalling and rough idle are among them. But what do these terms mean?

Engine stalling is when your car turns off when you slow down at an intersection, for instance. Sometimes this happens even when you are moving. Rough idle is when you feel strong vibrations while your car is idling.

These issues are not persistent. They tend to come and go. But don’t assume they will disappear permanently on their own. On the contrary, they may get worse if you don’t fix your coil soon enough.

6.   Hesitation of the Engine During Acceleration

You try to accelerate, and your car starts to spit and jerk. That is another example of engine misfiring. The same may happen when you drive fast.

The cause behind this symptom is often a damaged ignition coil. But do check your injectors too. Engine hesitation can also suggest that this part is faulty.

7.   Decreased Fuel Economy

Bad coils lead to engine misfires, and engine misfires lead to reduced fuel economy. Thus, one of the prominent faulty ignition coil symptoms is excess fuel consumption.

How to spot decreased fuel economy? Well, your trips to the gas station will become more regular.

8.   Increased Emissions

Increased emissions and reduced fuel economy go hand in hand. That is especially the case when the cause behind them is a faulty coil.

Some modern vehicles have a smart dashboard. It will notify you when emissions go up. But most car owners learn about the issue when they fail an emissions test.

9.   Failure or Struggle to Start the Car

Do you have trouble starting the engine? Various factors can lead to this issue. For instance, there may be insufficient charge in the battery. A clogged fuel filter or a bad ignition coil may have the same effect.

Visit your local auto repair shop to find the root cause of this. Also, try starting the car in cold weather. You will struggle to do that if the coil is damaged. An unusual noise upon engine start points to the same issue.

10.  Check Engine Light Goes On

The check engine light (CEL) can switch on for various reasons. One of them is a bad ignition coil. The CEL will pop up on your dash when you have continuously failed to notice the other telltale symptoms. By then, the issue may have started to affect other components of your vehicle.

How Long Do Ignition Coils Last?

Most manufacturers do not offer a replacement schedule for this car part. That suggests that coils may last for the entire lifespan of the vehicle. Yet, problems such as oil leaks and overheating may lead to their early “retirement.”

Often, the lifespan of the coil depends on that of the spark plug. In the past, spark plugs had platinum tips and their estimated lifespan was 60,000 miles.

Luckily, modern-day spark plug cylinders have tips made of iridium. This metal is several times stronger than platinum. So, they last for 100,000 miles. For your peace of mind, you can replace both components when you hit this number.

What Causes Critical Ignition Coil Symptoms?

Several key factors can damage the coil. You can prevent some of them, but others can be inevitable.

Engine Vibrations

The car engine creates vibrations when it is running. Over time, these vibrations can loosen spark plugs. That will put a strain on the coil because it must work extra hard to pass on the current. That may lead to overheating or electrical shorts.

Engine vibrations can also break parts of the ignition coil. In most cases, that results in coil insulation damages. Once again, that causes a short.

Worn-Out Spark Plugs or Spark Plugs Wires

The ignition coil often fails when there is a problem with its spark plug. It will send a higher voltage current if the plug’s wires or cylinders fail to work. When the voltage becomes too high, it compromises its insulation. That leads to a short.


Moisture causes ignition coil and spark plug failures. Even an A/C or oil leak can damage them considerably. A broken distributor cap can also have similar consequences.

Excessive Heat

Another factor that results in coil failure is the heat from the engine. When spark coils overheat, they struggle to conduct an electric current. Luckily, this is not something that happens often.

Large Spark Plug Gap

The more worn-out spark plug cylinders are, the more significant their gap will be. The distance between the spark plug’s electrodes increases. That forces the coil to send a higher voltage to them to make up for the gap. What follows next is coil overheating.

Resistance Changes

Variations in the resistance of the coil windings can also cause serious issues. If the resistance is very low, more electricity will flow through this part of the ignition system. That will hinder the cylinders from providing a strong spark. For that reason, the car may fail to start.

Can You Drive With a Bad Ignition Coil?

A faulty ignition coil alone won’t prevent your car from running. So, you can drive but you should not.

One defective coil can damage many other parts of your car. If you have a faulty coil, take steps to fix the issue now. That may save you a fortune later.

Failing to repair or replace this component on time can be very dangerous. The issue may become so severe that it may lead to a car fire.

How Much Will It Cost to Replace It?

The cost of replacing ignition coils depends on various factors. The year, model, and make of the automobile are a few of them. For example, retro car parts are hard to find. That is why they cost more.

The engine also affects the price of these repairs. Mechanics charge higher rates for piston engines with six cylinders or more. The coils of such cars are harder to get to, and that means higher labor costs.

The amount of money you will spend also depends on who will fix your vehicle. The cheapest option is to replace the part yourself, but you shouldn’t try that unless you know what you are doing.

Auto repair shops charge from $50 to $100 per hour for the labor. New coils cost between $70 and $300. That means that you won’t spend less than $100–$200. This price will be even higher if you rely on a dealership service.

A bonus pro tip: Change all your coils even if only one of them is defective. That will save you money on labor.

How to Prevent Bad Ignition Coil Symptoms?

Take care of this vehicle part to avoid high repair costs and faulty ignition coil symptoms. Follow the maintenance schedule that your car’s manufacturer recommends. Go to an auto repair shop now and then for a routine check.

Pay special attention to the spark plugs too. Their function is closely related to that of the coils. So, change them at the recommended time intervals.

Consider replacing the spark plug cylinders together with the faulty ignition coils. The more durable component of the two is the coil, and a damaged spark plug can reduce its lifespan.

Last but not least, address faulty ignition coil symptoms as soon as possible. That will help you nip many problems in the bud.

You may also like