Should I Replace a Car’s Ignition Coils With Spark Plugs?

If you’ve started to notice rough starts, misfires, or your car not quite running as it used to, you may have heard that both ignition coils and spark plugs are key culprits. Ignition coils and spark plugs work together to ignite the fuel-air mixture in your engine, but they wear out at different rates and serve distinct functions. So, should you be replacing them together?

Here’s what you need to know about each component’s purpose, signs of wear, and why it may (or may not) make sense to replace them at the same time.

Understanding Ignition Coils vs. Spark Plugs

Before diving into replacement advice, it’s helpful to get a grasp on what these parts actually do.

• Ignition Coils: Ignition coils transform your car’s battery voltage(12v) into the high voltage of about (20,000v) needed to create an electric spark in the spark plug. Each cylinder in most modern cars has its ignition coil. Without them, your spark plugs simply can’t function.
• Spark Plugs: Spark plugs are tiny but play a big role in how efficiently and smoothly your engine runs. They are positioned inside each cylinder to ignite the fuel-air mixture, causing combustion and powering your engine.

Both parts degrade over time. Ignition coils, exposed to high heat and wear, can fail every 50,000 to 100,000 miles depending on the car and driving conditions. Spark plugs, on the other hand, usually last 20,000 to 100,000 miles, depending on the type and make.

Do Ignition Coils and Spark Plugs Fail Simultaneously?

Though they work together, ignition coils and spark plugs don’t always wear out at the same rate. The wear on each can vary based on factors like engine design, the type of coil and plug used, and driving habits. So, it’s common for one part to wear out before the other.

• Symptoms of a Bad Ignition Coil: These include difficulty starting, engine misfires, reduced fuel efficiency, and poor acceleration. In some cases, you may even notice the “Check Engine” light come on via your dashboard.
• Symptoms of Worn Spark Plugs: Common signs include rough idling, difficulty starting, poor acceleration, misfires, and a decrease in fuel efficiency. Spark plugs often show more gradual symptoms as they wear out.

When Replacing Spark Plugs, Should You Replace the Ignition Coils Too?

Well, in this situation, It depends on the condition of each part, your vehicle’s age, and the symptoms you’re experiencing.

1. Routine Maintenance

If you’re just doing routine maintenance, it’s not strictly necessary to replace both. Spark plugs generally have a shorter lifespan than coils, so they may need to be replaced more frequently. If you’re changing the spark plugs as a preventative measure, inspect the ignition coils, but only replace them if they show signs of wear.

2. Experiencing Misfires or Poor Performance

If your engine is misfiring or running rough, it could be one or both components. Since misfires are commonly caused by either bad spark plugs or faulty ignition coils, it’s worth testing both. If you replace the spark plugs and continue to experience issues, then the coils are the likely culprit.

3. Cost Considerations

Replacing both ignition coils and spark plugs at the same time can save on labor costs if you’re having a mechanic perform the work, as they won’t have to open up the engine twice. This is especially true if your vehicle has coils and plugs that are challenging to access.

4. High Mileage or Older Vehicles

For older or high-mileage cars, it can be a good idea to replace both components simultaneously. This is a more proactive approach that ensures both systems are fresh and should function well for another long stretch.

Pros and Cons of Replacing Ignition Coils with Spark Plugs

Pros	Cons
Prevents potential misfires and engine issues	Adds extra cost if coils aren’t actually faulty
Saves on labor if done during the same service	Not necessary if coils are still in good condition
Can improve engine efficiency and performance	Could be overkill for newer cars
Proactive measure, especially for high-mileage cars	Could lead to unnecessary parts replacement

How to Test If Both Ignition Coils and Spark Plugs Need Replacement

Testing the health of each component can help you make an informed decision.

1. Diagnostic Tool Check: Many modern vehicles can identify which component is faulty through diagnostic codes accessible via an OBD-II scanner. If your car’s “Check Engine” light is on, the code may pinpoint the exact cylinder or issue, letting you know if it’s the coil, plug, or something else entirely.
2. Visual Inspection: Spark plugs can be removed and inspected for wear. Look for signs like erosion, discoloration, or carbon buildup. Ignition coils, though harder to visually inspect for wear, can sometimes show cracks or corrosion if they’re faulty.
3. Testing Resistance on Ignition Coils: With a multimeter, you can check the resistance on each ignition coil. If the readings don’t match the specifications in your car’s manual, the coil likely needs replacing.

Final Thoughts

In summary, replacing both spark plugs and ignition coils is not always necessary, but it can be a practical option in certain situations:

• If your car is experiencing misfires or other performance issues, replacing both may solve the problem and prevent further inconvenience.
• For high-mileage vehicles, changing both parts can enhance longevity and reliability.
• If you’re simply changing spark plugs as part of routine maintenance, inspect but don’t feel obligated to replace the ignition coils unless they’re showing signs of wear.

Taking a proactive approach can sometimes mean replacing more than necessary, but if it means peace of mind and optimal performance, and it’s often worth the investment.