Ignition Coil Vs. Spark Plug – The Differences To Know

There are so many cars and drivers on the road every day, but only a few know the difference between an ignition coil vs. spark plug. Some do not even know these components exist. It’s essential to know that both are ignition system components but performs different functions. 

This article will explain ignition coils, spark plugs, their differences, causes of failures, and symptoms. I’ll also discuss ignition coil vs. spark plug wires. But first, let’s see what ignition coil and spark plugs do in an engine.

ignition coil and spark plug

Ignition Coil Explained

An ignition coil is an essential ignition system component that ensures a successful ignition of an internal combustion engine. Manufacturers designed ignition coils to receive low electricity from the car battery and transform it into volts required to provide sparks in the combustion chambers.

It is an induction coil in the car’s ignition system that has an outer and inner coil. It creates the spark used by the plugs in the combustion chamber.

The ignition system has evolved over the years. Therefore, the inner workings of 1980s vehicles are different from today’s vehicles. Cars have two ignition systems – the primary and the secondary ignition.

When you turn on the car engine, it triggers the primary ignition, which activates the circuit between the ignition coils and the battery, transmitting electric flow back and forth among themselves. The electric flow between the ignition and the battery creates a magnetic field in the ignition coil.

The magnetic field activates the secondary ignition, which briefly interrupts the magnetic field to create an electrical current between the outer and inner coils. This converts the original 12 volts from the car battery to over 50,000 volts to create the required sparks in the combustion chamber.

I know you’ll be wondering why such high voltage. This is because the plugs need such high voltage to carry out their duty effectively.

what does an ignition coil do

Spark Plug Explained

The spark plug is an essential ignition system that sends the required spark into the combustion chamber to ignite the air-fuel mixture. The ignition in the cylinder bores kicks off the combustion process, which forces the pistons up and down, creating the power to move the vehicle.

After the ignition coils convert the 12 volts from the car battery to over 50,000 volts, it sends it to the spark plugs. The plugs create a spark with this current in the gap between its electrodes to ignite the air-fuel mixture in the combustion chamber.

Having explained the meaning and functions of the ignition coil and spark plug, let’s compare spark plugs versus ignition coils to see their differences.

can a bad coil pack ruin a spark plug

Ignition Coil Vs. Spark Plug Differences

While spark plugs and ignition coils are essential parts of the ignition system that work in harmony, they are not the same. They have different functions. It is important to note that these ignition system components are only available in a gasoline-powered vehicle.

Diesel engines do not use spark plugs and ignition coils because they do not ignite via spark but through compression. Therefore, they replace spark plugs with glow plugs.

I have digressed a little from the main subject. Back the ignition coils or coil packs vs. spark plugs.

  • Ignition coils receive power from the car battery, while spark plugs receive electric voltage from the ignition coils.
  • Ignition coils receive 12 volts, while the spark plugs receive 50,000+ volts.
  • Ignition coils transmit the voltage to the plugs, while the spark plugs ignite the air-fuel mixture in the combustion chamber.

The explanation and differences show that the ignition coils and spark plugs complement each other. For this reason, bad spark plugs and ignition coil symptoms are difficult to separate from each other. They share several symptoms.

For example, if your car is losing power, misfiring, idling poorly, or the engine warning light appears on the dashboard, it could mean you have bad spark plugs. A failed ignition coil will also emit these symptoms, making it difficult to detect if you have faulty coils or misfiring plugs without proper diagnosis.

How do you know if you need spark plugs or coil packs?

Since lousy spark plugs and ignition coils share the same symptoms, the only way to know if you need spark plugs or coil packs is by testing them. If you are asking how do I know if my ignition coil or spark plug is bad, there are a few ways of testing them regardless of the ignition system you have.

You can test the ignition coils by using a specialized test light or spark tester. You’ll connect the tester to the ignition coil wiring harness, which will light up when current flows through it.

Another easy method is to test the coil’s outer and inner resistance. If the result is not within the specified range, you have a dead coil that needs replacement. Meanwhile, it’s important to note that a malfunctioning coil can still be within the specified range.

One common way to check if the ignition coil or plug is faulty is by swapping them. If no.1 cylinder is misfiring and you’re unsure if it is the coil or plugs, swap the ignition coil to the cylinder you know is working correctly. If the swapped coil works appropriately on the other cylinder, you likely have a bad plug that needs replacement.

But if it doesn’t work on other cylinders, the coil is bad. To test the spark plug, connect a good coil to the no.1 cylinder and see the outcome. If it works fine, the plug is okay, and if it doesn’t, replace or clean the plugs.

As reiterated above, plugs and ignition coil failure cause poor idling, illumination of check engine light on the dashboard, poor acceleration, engine misfiring, car hesitation or vibration, hard starting, and poor gas mileage. So, it is vital to resolve a bad ignition coil or plugs to enjoy a seamless ride.

Frequently Asked Questions – FAQs

Q: When should spark plugs and coils be replaced?

Typically, ignition coils should be replaced every 80,000 to 120,000 miles. And spark plugs come in various types. We have conventional and long-life spark plugs. The conventional plugs last between 30,000 to 50,000 miles, while the long-life (platinum or Iridium plugs) last between 60,000 to 120,000 miles, depending on your car.

You can find this information in your car owner’s manual or the service booklet. However, spark plugs and ignition coils can fail before the recommended time. And you should replace them whenever they fail, whether it is up to the recommended interval or not.

Q: Will a bad ignition coil foul spark plugs?

Yes, a bad ignition coil can foul the spark plug in that cylinder. Meanwhile, a fouled spark plug doesn’t necessarily mean the plug is dead and needs replacement. When you hear a fouled spark plug, it means the plug is covered with substances like oil, fuel, carbon, or any contaminants that prevent it from running as it should. You can clean and reuse the spark plug.

However, fouled spark plugs can cause severe drivability issues like poor idling, poor acceleration, bad gas mileage, engine hesitation and vibration, engine warning light, and engine misfiring.

Q: Can you replace ignition coils without replacing spark plugs?

When asking, should I change ignition coils with spark plugs? The answer depends on the condition of both ignition components. If the spark plugs wear out due to a faulty coil, you have to replace both at the same time. But if one of these components fails and the other is still in good condition, replace only the lousy one.

Q: What kills an ignition coil?

Several factors can cause ignition coils to fail. However, the common cause of its failure is due to wear and tear because of its location. It is located on top of the engine, one of the hottest parts under the hood. As a result, it is exposed to high temperature and vibration, making them susceptible to failure. Other probable causes include poor electrical connections, faulty modules, or poor groundings.

Q: What happens if you don’t change spark plugs and coils?

Spark plugs and ignition coils are not designed to last the lifespan of the engine. They’ll fail over time and needs ignition coil and spark plug replacement. If you fail to replace them when they degrade, they’ll not provide enough spark to ignite the air-fuel mixture properly.

As a result, they will cause several drivability issues like poor acceleration, rough idling, hard starting, the illumination of the check engine light on the dashboard, loss of engine power, and in severe cases, the vehicle may stop you in the middle of nowhere.

Final Words

The ignition coil vs. spark plug will tell of several ways to narrow down to each component and know which one is faulty despite the same symptoms when both the components become faulty. Regardless of the faulty part, you may have to replace the plugs. If you replace the plugs, and that doesn’t fix the problem, you have lousy ignition coils.

Follow the diagnosing process above if you don’t want to replace the plugs when they are still working correctly.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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