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When to Replace an Ignition Coil: 8 Signs to Look For

Ignition Coil

Ignition coils convert the 12-volt current from a car battery to the approximately 20,000 volts required to spark the engine. This is to give it enough of a spark to ignite the fuel in the engine. Every spark plug in an engine is connected to an ignition coil, which is either wired to the plug or sits directly on top of it. It can cost several hundred dollars to have one replaced, but you may be able to replace it yourself to save some money.

Below, we have included eight symptoms of a failing or failed ignition coil, although most of these problems can have other causes, so it is worth having checked out by a professional mechanic if you do experience and road divider

The 8 Signs to Look For if Your Ignition Coil Is Faulty

1. Difficulties Starting the Engine

Because the ignition coil is primarily involved in starting the engine, one of the first symptoms you will experience when you have a bad engine coil is difficulty starting the engine. If you have a single faulty coil, you may find that your engine does start. However, you hear it misfiring, and it takes a long time before the ignition kicks in.

There are many reasons you might have problems starting a car, though, so this symptom alone does not guarantee that you have a faulty coil.

car engine of an orange car
Image Credit: Photoman, Pixabay

2. Misfiring Engine

When an engine misfires, it will usually lose power. It most often occurs when the engine is under heavy load, which means when you’re accelerating hard or at the high end of the rev counter, also known as the tachometer. It can also occur when first starting the engine. As well as hearing a sputtering sound, you will likely feel a jolt when the engine misfires, meaning that one of the cylinders is not firing properly.

Again, as with difficulties starting the engine, there are other causes of a misfiring engine, and it may not necessarily indicate faulty coils.

3. Stalling

When a coil is faulty, the spark plugs are not getting the necessary spark they need to fire. This means that as you let go of the clutch and push the accelerator down, you won’t get the power you need. This can result in the car stalling, which will typically happen just after you’ve started the car or when pulling away from junctions.

If this is coupled with problems starting the engine, also caused by failing coils, you could be stuck on the side of the road with no way to move.

honda car engine
Image Credit: artellliii72, Pixabay

4. Backfiring Engine

Backfiring is caused when unburned fuel passes through the exhaust pipe. It is accompanied by a loud bang and will usually have grey emissions from the tailpipe. A backfiring engine can result in serious damage to the car if you don’t remedy the problem soon, so you should always have this problem investigated.

5. Lower Fuel Economy

If your spark plugs aren’t delivering enough power to fire the cylinders, the engine will pump more gas through to try and create the power it needs. This not only causes backfiring, but it means that the engine is needlessly pumping more gas out. Your fuel consumption will increase, and your fuel economy will drop. If you are filling the tank up more often than normal or your dash indicates that your miles per gallon have dropped, this is a possible sign that your ignition coils are failing.

man refueling his car
Image Credit: RossHelen, Shutterstock

6. Lack of Power

Because the spark plugs aren’t delivering enough power and unspent fuel doesn’t increase the amount of power you’re getting, you may notice a drop in power. The car can start to feel sluggish, and you won’t enjoy the same responsiveness when you put your foot on the gas. Other problems, like a faulty injector, can cause similar performance issues.

7. Check Engine Light

The check engine light is a useful warning light that means something is amiss under the hood. While this light could mean any of a series of problems, one of those potential problems is a wrecked ignition coil. If your light is on and you are experiencing more of the symptoms in this list, get your engine checked for possible faults.

check engine light
Image Credit: virgmos, Shutterstock

8. Smell of Gas From The Exhaust

This is another symptom that is caused by the engine injecting more gas to make up for a lack of power from the spark plugs. The gas is not burned before it is exhausted from the tailpipe, causing increased emissions and a smell of unburned gas. This is often accompanied by backfiring and misfiring, but if there is a noticeable smell of gas, you need to have your car checked for and road divider

Can You Drive With a Bad Ignition Coil?

If left untreated, a problem with the ignition coil can cause further damage to the car. If the car still runs, however, you should be OK to drive it to a mechanic or on a short journey home.

driver starting the car engine
Image Credit: lzf, Shutterstock

How Long Do Ignition Coils Last?

How long an ignition coil lasts depends on a lot of factors, but you can expect one to last for around 100,000 miles before it requires maintenance.

What Causes Engine Coil Failure?

Engine coils, like all mechanical parts, won’t last forever. Wear and tear, which occurs through general use, is the single biggest reason for one to fail. Damage to your spark plugs may also result in damage to the coils, while excessive vibrations or engine overheating problems can also have the same result.

car and road divider


Like other mechanical parts of a car, the engine coil will become worn over time, which can cause it to fail or perform poorly. This can lead to symptoms including problems starting the car, stalling, and a loss of power and fuel economy. If you know your way around a car engine, you may be able to replace the coil, which is either attached by wires or directly to the spark plugs, yourself. Alternatively, an experienced mechanic will be able to do the work for you and have you back on the road in a few hours.

Featured Image Credit: MuhammadIbrar, Pixabay


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