Bad Coil Pack Symptoms: Everything You Need To Know

Ignition coils are a crucial part of your vehicle’s engine. They generate the voltage that powers the spark plugs, igniting the fuel in your car’s cylinders.

However, when bad coil pack symptoms arise, it can lead to some major issues with your vehicle. Here we’ll look at what causes them to fail and what symptoms you should watch out for before replacing them.

How an Ignition Coil Works

Ignition coils are part of the ignition system. The ignition coil is a device that converts the 12-volt power of the vehicle’s electrical system into the high-voltage current needed to spark the fuel in the cylinder.

Car mechanic replacing ignition coil on gasoline engine.

The ignition system consists of several components and circuits working together to give you a smooth start-up and running engine once it is started. The most important parts of this system are:

Spark plug

This is where combustion takes place. It generates sparks causing an explosion inside your engine, which creates energy that pushes pistons down, creating rotational motion and turning the crankshaft (which then turns wheels).

Ignition distributor

This controls when the spark happens by sending out electrical pulses from its rotor arm; when the spark happens depends on the timing advance mechanism inside the distributor; when timing advance mechanism sends the signal through a wire connected between it and the car computer (ECU), ECU tells distributor “spark now!”

Then distributor activates the spark plug at right time through electric current coming from the battery or generator via coil pack harnesses/wires going through electric motor-driven wires.

Other factors may involve, like vacuum leak detection, etc., but this is how it works conceptually.

Symptoms of a Bad Ignition Coil

Ignition coils are susceptible to a variety of problems, including but not limited to:

  • Backfiring
  • Poor engine performance
  • Engine stalls (especially at idle)

What is Backfiring?

Backfiring is a loud noise that sounds like a gunshot and it can be caused by a bad spark plug, a bad ignition coil, or a bad fuel injector. The most common cause of backfiring is when the spark plug fires before the piston reach the top dead center (TDC) on its compression stroke.

Close-up of an old fuel injector.

Because this happens before the air-fuel mixture has been fully compressed by combustion pressure in the cylinder at TDC, unburned fuel ignites prematurely and causes backfiring.

Backfiring can also occur when there’s too much fuel injected into the cylinder during the intake stroke. This causes an excess amount of unburned fuel to exit through your exhaust tract whenever more than one cylinder backfires at once due to engine misfire issues or incorrect timing settings on your car’s ignition system.

What Does It Mean When Your Engine Is Hard to Start?

If you put your key in the ignition and your car doesn’t start right, or it takes several tries to start up, you may be experiencing symptoms of a bad coil pack. The most common cause of this is a bad spark plug. If your engine has multiple spark plugs, one or more may be misfiring due to worn-out electrodes.

This makes it difficult to start your vehicle and can cause idling issues or rough running if the problem persists. There are other causes of hard starting, such as a dirty or faulty fuel injector. These may also be culprits if you’ve recently installed new spark plugs or have noticed a drop in gas mileage.

Signs of a Poor Fuel Economy

Empty gas fuel tank indicator on car dashboard.

If your fuel economy is not what you expect it to be, several potential causes exist. One possibility is that your vehicle has a bad ignition coil. If this happens to be the case, you may notice some of the following symptoms:

  • Lack of acceleration when starting from a stop
  • Decreased power overall
  • Engine misfires

Vehicle Stalling

The vehicle may also experience stalling, which is a sign of a bad ignition coil. Several factors can cause stalling, and you mustn’t ignore this symptom as it could be dangerous. You cannot accelerate or change gears properly when driving your car stalls. This can lead to an accident if another driver rear-ends you.

In addition, faulty coils require replacement more quickly than others which means that they are more expensive to replace.

Check Engine Soon Light

The check engine soon light is a warning light, not a diagnosis. It’s not a repair, fix or cure. The light means that there is an issue with your car and it requires further inspection by an auto mechanic to determine the problem.

Many different issues, including these can cause the check engine soon light:

  • A bad ignition coil (if you are experiencing this issue)
  • A bad O2 sensor (if you are experiencing this issue)
  • Low fuel pressure in the fuel rail (if you are experiencing this issue)
  • Electronics going out in the vehicle

Average Ignition Coil Replacement Cost

Ignition coils are also known as spark plugs and are an important part of your car’s engine. They’re responsible for creating a spark that fires when the voltage from your alternator flows through them. The ignition coil can fail at any time for several reasons, but it’s usually caused by age or physical damage that makes it unable to work properly.

If you notice some signs that your ignition coil is going out, it may be time to replace it before things get worse—and soon enough, you’ll find yourself looking at average costs between $168 and $218 for replacement parts! If you cannot replace the coil yourself, the average labor cost is between $51 and $64.

When to Get a Vehicle Check

Ignition coils are an important part of your vehicle’s engine. If they fail, it can cause a variety of symptoms. For example, your check engine soon light might pop on along with your vehicle starting to get poor gas mileage. Your car might even start stalling.

If you experience any issues with your ignition coil, it’s best to have them replaced right away by a professional. If you have questions about your vehicle’s bad coil pack symptoms, then drop them in the comments below.

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About Brock Rangel

Hi, I am Brock, and I am the lead editor/photographer for TheCarColony. I have been a mechanic for over 14 years now, and I am here to spread my car knowledge across the web!

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