What is a symptom of a bad ignition coil?

A bad ignition coil can cause several noticeable symptoms in a vehicle. The ignition coil is a critical component in the vehicle's ignition system, responsible for providing the high-voltage spark that ignites the air-fuel mixture in the engine's cylinders. When the ignition coil fails, it can lead to various performance issues and problems.

Common Symptoms of a Bad Ignition Coil

• Misfiring engine: A malfunctioning ignition coil can cause the engine to misfire, resulting in a rough, uneven running engine. This can be felt as a jerking or shuddering sensation while driving.


• Reduced engine performance: A bad ignition coil can lead to a loss of power and acceleration, as the engine is not receiving the proper spark to efficiently combust the fuel.


• Difficulty starting the engine: If the ignition coil is failing, it may not be able to provide the necessary voltage to start the engine, making it difficult or impossible to start the vehicle.


• Check engine light illumination: The vehicle's onboard diagnostic system will typically detect a problem with the ignition coil and illuminate the check engine light on the dashboard.


• Decreased fuel efficiency: A malfunctioning ignition coil can cause the engine to run less efficiently, leading to reduced fuel economy.

These are the most common symptoms associated with a bad ignition coil. If you experience any of these issues, it's important to have your vehicle inspected by a qualified mechanic to diagnose and address the problem.

How to tell if a coil needs replacing?

You can tell a coil needs replacing by observing symptoms like poor performance, such as a burnt taste from a vape or engine misfires in a car. Other signs include a decrease in vapor or power, an illuminated "check engine" light, leaking, or unusual sounds like gurgling or backfiring. A visual inspection for physical damage like cracks, and using a diagnostic scanner to check for specific codes can also confirm a bad coil. 
For a vehicle ignition coil

• Check Engine Light: An illuminated light on the dashboard is a common indicator of an ignition system issue. 
• Engine Misfires: You may feel the engine shudder, jerk, or run unevenly, especially during acceleration. 
• Rough Idle: The engine may shake or vibrate noticeably when the car is stopped. 
• Difficulty Starting: The engine may take longer to crank before starting or might not start at all. 
• Reduced Power: You might notice a loss of power when accelerating or a general sluggishness. 
• Poor Fuel Economy: The engine may burn fuel inefficiently, leading to worse gas mileage. 
• Backfiring: A sudden backfire (a loud pop) can occur if unburnt fuel ignites in the exhaust system. 
• Visual Damage: Look for physical damage like cracks in the coil's housing or oily residue around it. 
• Diagnostic Codes: An OBD-II scanner can read trouble codes (like P0300) that point to a specific cylinder misfire. 

For a vape coil

• Burnt Taste: This is the most common sign, as the cotton wicks and coil element wear out over time. 
• Diminished Flavor: Your e-liquid may not taste as good or the flavor profile becomes weaker. 
• Reduced Vapor: Your device produces less vapor than it used to. 
• Gurgling Sounds: A hollow bubbling sound can indicate the coil is having trouble and needs replacing. 
• Leaking: A worn-out coil can cause the e-liquid to leak from the device. 
• Darker E-juice: The color of your e-liquid might darken prematurely. 
• Airflow Clogging: You may notice the airflow feels restricted or clogged. 

How do you tell if your ignition coil is bad?

A bad ignition coil can be identified by symptoms like a flashing check engine light, engine misfires (causing jerking, sputtering, or a rough idle), sluggish acceleration, and difficulty starting the engine. You may also notice poor fuel economy or hear a loud backfiring sound from the exhaust, which can happen when unburned fuel ignites.
 
Common symptoms of a bad ignition coil 

• Check engine light: A check engine light on your dashboard is a common sign that the car's computer has detected a problem, often an ignition system issue. 
• Engine misfires: This can feel like a coughing or sputtering sound, a strong vibration, or a jerking sensation, especially when accelerating. 
• Rough or shaky idle: The engine may run unevenly and vibrate when the vehicle is stopped or idling. 
• Sluggish acceleration: The vehicle may hesitate and feel slow to accelerate because the engine isn't getting enough power. 
• Difficulty starting: The car may crank for a long time before starting, or fail to start altogether. 
• Poor fuel economy: The engine may use more fuel than usual because it is not combusting efficiently. 
• Backfiring: A loud bang from the exhaust is caused by unburned fuel entering and igniting in the exhaust system. 

How to confirm (advanced)

• Use an OBD-II scanner: A mechanic can use this tool to read specific misfire codes (e.g., P0300-P0308) that pinpoint which cylinder is misfiring, providing strong evidence of a faulty coil. 
• Test resistance: A mechanic can measure the resistance of the ignition coil with a multimeter to see if it falls within the manufacturer's specified range. A reading of zero ohms often indicates a shorted coil. 

Can a bad ignition coil cause rough idle?

Yes, a bad ignition coil can absolutely cause a rough idle. A faulty coil fails to deliver a consistent or strong spark to the spark plug, leading to an engine misfire and causing the engine to run unevenly, shake, or vibrate while idling. 
This video explains the symptoms of a bad ignition coil and how they lead to rough idling: 53sFixITYouTube · Apr 11, 2024

• Misfiring: A bad ignition coil can cause one or more cylinders to misfire, meaning they don't combust the air-fuel mixture correctly. 
• Uneven combustion: This inconsistent combustion makes the engine idle unevenly and can be felt as a shake or vibration at idle. 
• Other symptoms: A rough idle is often accompanied by other signs of a failing ignition coil, such as a check engine light, reduced engine power, difficulty starting, and decreased fuel efficiency. 

This video explains how a faulty ignition coil can cause a rough idle: 59sMechanical SpecialYouTube · Jan 30, 2024

What does a car do when it has a bad coil?

One of the most common symptoms associated with a faulty ignition coil is engine performance issues... Faulty coils may cause the vehicle to experience misfires, a rough idle, a loss in power and acceleration, and a reduction in gas mileage. In some cases the performance issues may even result in the vehicle stalling.