What are the symptoms of a bad ignition coil on a Subaru?

If you own a Subaru, it's important to be aware of the potential symptoms of a bad ignition coil. The ignition coil is a critical component in your vehicle's ignition system, responsible for providing the high-voltage spark that ignites the air-fuel mixture in your engine's cylinders. When an ignition coil fails, it can lead to a range of performance issues and even cause your engine to stall. In this article, we'll explore the common symptoms of a bad ignition coil on a Subaru, so you can identify the problem and take the necessary steps to address it.

Misfiring Engine

One of the most obvious signs of a bad ignition coil is a misfiring engine. When an ignition coil fails, it can't provide the necessary spark to ignite the air-fuel mixture in one or more cylinders, leading to a rough, uneven engine performance. You may notice the engine stuttering, hesitating, or even stalling, especially during acceleration or under load.

Reduced Fuel Efficiency

A malfunctioning ignition coil can also lead to reduced fuel efficiency in your Subaru. When the engine is not firing correctly, it's not burning the fuel as efficiently as it should, resulting in decreased fuel economy. You may notice a drop in your vehicle's miles per gallon (MPG) if you have a bad ignition coil.

Check Engine Light Illumination

Another common symptom of a bad ignition coil is the illumination of the check engine light on your Subaru's dashboard. The vehicle's onboard diagnostic system will detect the issue with the ignition coil and trigger the check engine light to alert you of the problem.

Difficulty Starting the Engine

If your Subaru is having trouble starting, it could be a sign of a bad ignition coil. When the coil is failing, it may not be able to provide the necessary spark to start the engine, leading to a no-start or hard-start condition. This can be especially noticeable in cold weather or when the engine is under load.

Rough Idling

A bad ignition coil can also cause your Subaru's engine to idle roughly. The uneven firing of the cylinders due to the coil failure can result in a rough, unsteady idle, which may be accompanied by vibrations or a shaking sensation in the vehicle.

If you're experiencing any of these symptoms in your Subaru, it's important to have your vehicle inspected by a qualified mechanic as soon as possible. Ignoring a bad ignition coil can lead to further damage to your engine and other components, so it's best to address the issue promptly.

How to check if your ignition coil is bad?

You can check for a bad ignition coil by observing vehicle symptoms like a check engine light, engine misfires, or poor performance, then testing for a spark or using a multimeter to measure resistance. A simple way to test a coil on each plug is to disconnect one at a time and listen for a change in engine misfiring, as unplugging a good coil will make the engine run worse, while the engine won't change if the coil is bad. 
Initial symptom checks

• Check engine light: A blinking or solid check engine light can indicate a misfire caused by a failing coil. 
• Engine misfires: Your engine may feel like it's "coughing," sputtering, or jerking. 
• Performance issues: You may notice decreased acceleration, power, or fuel efficiency. 
• Rough idle: The engine may idle roughly or stall, especially at idle or when it gets hot. 
• Backfiring: Unburnt fuel can ignite in the exhaust system, causing loud popping sounds. 

Diagnostic tests

• Spark test: For a coil-on-plug system, remove the coil and plug boot, connect it to the spark plug, and hold the plug near a ground. With the wiring connector attached, crank the engine to check for a strong, blue spark. No spark indicates a problem with either the coil or the wiring. 
• Multimeter test: Disconnect the coil and set your multimeter to the appropriate resistance (ohms) setting. Touch the probes to the coil's terminals (check your vehicle's service manual for the correct terminals). Readings that fall outside the specified resistance range indicate a faulty coil. 
• Cylinder drop test: With the engine running, unplug the ignition coil connector from one cylinder at a time. 
  • If the engine's running changes (e.g., misfires worse), that coil is likely good. 
  • If unplugging the coil causes no change in the engine's performance, you've likely found the bad coil. 

What to do if you suspect a bad coil

• If the test indicates a problem, the coil needs to be replaced. 
• It's possible that other issues like bad spark plugs or wiring are causing the symptoms, so have those checked as well. 
• When replacing a coil, always use a high-quality replacement part. 

How do I know if my Subaru coil pack is bad?

4 Signs of a Faulty Ignition Coil

1. Misfires. Think of the ignition coil as the conductor of an orchestra, ensuring each spark plug fires in harmony.
2. Poor Fuel Economy.
3. Warning Lights.
4. Unusual Smells.
5. Get Your Ignition Coil Repaired by Your Subaru Dealer.

Why do subarus sound like they are misfiring?

Problems with fuel injectors, fuel pumps, or even the fuel filter can cause an uneven fuel supply, leading to misfires. Air intake and exhaust issues: A proper air-fuel ratio is essential for efficient combustion.

What is a common symptom of a failing ignition coil?

Symptoms of a bad ignition coil include engine misfires, rough idling, and a check engine light. Other signs are sluggish acceleration, poor fuel economy, difficulty starting, and engine stalling. You might also notice sputtering, backfiring, or a strong smell of gas.
 
Performance and starting issues

• Engine misfires: The engine may feel like it's coughing, sputtering, or shaking because a spark plug isn't firing correctly. 
• Rough idling: Your car may shake or vibrate noticeably when it's stopped, such as at a traffic light. 
• Poor acceleration: You may experience sluggishness or a noticeable loss of power when trying to accelerate. 
• Difficulty starting: The engine may struggle to start, or may not start at all if multiple coils are bad. 
• Stalling: The engine may stall or hesitate while driving. 

Efficiency and other indicators

• Decreased fuel economy: A bad coil can cause the engine to burn more fuel, so you'll get fewer miles per gallon. 
• Backfiring: You might hear loud banging noises from the exhaust, which occurs when unburned fuel ignites in the exhaust system. 
• Strong smell of gas: This can happen when unburned fuel escapes through the exhaust system. 
• Check engine light: The vehicle's computer will detect the misfire and turn on the check engine light. A mechanic can use an OBD2 scanner to read the specific error codes.