Should You Change Ignition Coils with Spark Plugs?
You’re turning the key in your car, expecting that familiar roar, but instead, the engine sputters or doesn’t start at all. That’s what happened to me a few summers ago with my Chevy Silverado. I figured the spark plugs were due for a change, but then I started wondering about the ignition coils. Should I replace those too? It’s a common question for DIYers and car owners trying to save money while keeping their ride in top shape.
I’ve been down this road, replacing plugs and coils on my truck and helping friends with their cars. Let’s dive into whether you should change ignition coils with spark plugs, why it might matter, and how to make the right call for your vehicle.
Photo by firestonecompleteautocare
Spark Plugs and Ignition Coils
Before we get into whether you should replace both, let’s talk about what these parts do. Spark plugs are small but mighty. They screw into your engine’s cylinders and create a spark to ignite the air-fuel mixture. That spark is what makes your engine run. Plugs wear out from heat, carbon buildup, and electrical arcing. I’ve noticed my truck starts misfiring or idling rough when the plugs are worn.
Ignition coils are the unsung heroes. They take the battery’s low voltage and boost it to thousands of volts to make the spark plug fire. Most modern cars have one coil per cylinder, called a coil-on-plug system. Older cars might use a single coil or a distributor setup.
Coils are tougher than plugs but can fail from heat, vibration, or age. I had a coil go bad on my Chevy once, and it felt like the engine was choking—misfires, rough idle, the works.
Spark plugs usually last 30,000 to 100,000 miles, depending on whether they’re copper, platinum, or iridium. Ignition coils can go 100,000 miles or more, but they don’t have a set schedule. So, replacing spark plugs doesn’t always mean you need new coils. But there are times when it’s a smart move.
Why Consider Changing Ignition Coils with Spark Plugs?
I’ve learned that replacing ignition coils with spark plugs isn’t always necessary, but it can save you time and trouble in certain cases. Here’s why I sometimes do both at once:
High Mileage
If your car has over 100,000 miles, the coils might be nearing the end of their life. When I changed the spark plugs on my buddy’s 2008 Ford Focus at 130,000 miles, we swapped the coils too, since they were original and starting to act up.
Preventive Maintenance
Replacing coils with plugs can prevent future breakdowns. I hate pulling the engine apart twice, so if the coils are old, I’ll swap them to avoid another repair soon.
Misfire Issues
If your engine’s misfiring, it might not just be the plugs. A bad coil can cause the same symptoms. I learned this when my Chevy kept misfiring even after new plugs—turns out, one coil was shot.
Labor Savings
If you’re paying a mechanic, labor costs for spark plug replacement are similar to replacing coils. I saved a few bucks by doing both at once on my sister’s Honda Civic.
Warranty Matching
Some coils come with a warranty that matches the spark plug replacement interval. If you’re replacing plugs at 60,000 miles, new coils might be covered for the same period.
On the flip side, if your coils are working fine and your car’s under 80,000 miles, you probably don’t need to replace them. I’ve skipped coil replacement on newer cars with no issues.
Signs Your Ignition Coils Need Replacing
How do you know if your coils are bad? I’ve dealt with faulty coils a few times, and the symptoms are hard to miss once you know what to look for. Here’s what I check:
Misfires: The engine feels like it’s stuttering or shaking, especially under acceleration. I noticed this in my Chevy when one cylinder wasn’t firing right.
Rough Idle: The car vibrates or feels unsteady when stopped. My friend’s Toyota Camry had this, and a bad coil was the culprit.
Check Engine Light: A flashing or steady light often means a misfire. I use a $20 OBD2 scanner to pull codes like P0301, which points to a specific cylinder’s coil or plug.
Poor Fuel Economy: If your gas mileage drops, a weak coil might be causing incomplete combustion. I saw this on my wife’s SUV before we replaced a coil.
Hard Starting: The engine struggles to start or takes longer to crank. This happened to my Chevy when a coil was failing.
Visible Damage: When I pull spark plugs, I check the coils for cracks, corrosion, or burn marks on the boot or housing. A cracked coil on my truck was letting moisture in, causing misfires.
If you see these signs, test the coils before replacing them. I’ll explain how to do that later.
When to Stick with Just Spark Plugs
Not every spark plug change needs new coils. I’ve skipped coil replacement plenty of times with no regrets. Here’s when I stick to just plugs:
Low Mileage: If your car’s under 80,000 miles, the coils are likely fine unless you see symptoms. My 2015 Subaru had 50,000 miles when I changed the plugs, and the coils were still perfect.
No Symptoms: If the engine runs smoothly, gets good mileage, and has no check engine light, the coils are probably okay. I check for issues before spending extra.
Budget Constraints: Coils can be pricey—$20 to $100 each, depending on the car. If money’s tight, I test the coils and only replace the bad ones.
Recent Coil Replacement: If you’ve replaced coils recently, there’s no need to do it again. I keep records of my repairs to avoid doubling up.
The key is to know your car’s condition. If it’s running fine, save the cash and just do the plugs.
How to Test Ignition Coils
I always test coils before replacing them—it saves money and hassle. Here’s how I do it, based on my garage experiments:
Visual Inspection: Pull the coils when you change spark plugs. Look for cracks, burn marks, or corrosion. I found a cracked coil boot on my Chevy that was causing a misfire.
Swap Test: If you suspect a bad coil, swap it with another cylinder’s coil and see if the misfire moves. I did this on a friend’s Ford, and it pinpointed the faulty coil.
Multimeter Test: Use a multimeter to check the coil’s resistance. Primary resistance should be 0.4–2 ohms, and secondary resistance should be 6,000–10,000 ohms (check your car’s specs). I bought a $20 multimeter for this, and it’s been a lifesaver.
OBD2 Scanner: Plug in a scanner to read misfire codes. My scanner showed a P0302 code (cylinder 2 misfire), which led me to a bad coil.
Professional Test: If you’re not sure, take it to a mechanic. AutoZone or similar shops often test coils for free. I’ve used their testers when I didn’t have my tools handy.
Testing takes 20–30 minutes and can save you from replacing good coils. I’ve caught bad coils this way and avoided unnecessary costs.
Costs of Replacing Ignition Coils and Spark Plugs
Replacing coils and plugs can add up, so here’s a table of typical costs based on my experience:
| Item | Estimated Cost (USD) | Buy Now |
|---|---|---|
| Spark Plugs (per plug) | $5–$25 (copper, platinum, iridium) | Check Price on Amazon |
| Ignition Coils (per coil) | $20–$100 | Check Price on Amazon |
| Labor (mechanic, per hour) | $80–$150 | Hire Locally |
| DIY Tools (multimeter, scanner) | $20–$50 | Check Price on Amazon |
For my Chevy (6-cylinder), I spent $60 on spark plugs and $150 on coils for a DIY job. Labor would’ve added $100–$200 at a shop. Costs vary by car—luxury models like BMWs have pricier parts.
Benefits of Replacing Both Together
I’ve found some real perks to swapping coils and plugs at the same time, especially on older cars:
Saves Time: You’re already pulling the coils to get to the plugs in most cars. Replacing both means one job instead of two. I saved an hour by doing both on my truck.
Prevents Repeat Issues: Old coils can fail soon after new plugs, causing the same misfire. I learned this when my friend’s Honda needed another repair a month after new plugs.
Improves Performance: New coils and plugs make the engine run smoother, boost power, and improve gas mileage. My Chevy felt peppier after a full swap.
Matches Lifespan: If you’re using long-life plugs (like iridium, good for 100,000 miles), new coils ensure everything lasts the same amount of time.
But don’t just throw money at coils if they’re fine. Test them first to be sure.
Risks of Not Replacing Faulty Coils
I’ve seen what happens when you ignore bad coils, and it’s not pretty. Here’s why you shouldn’t skip them if they’re failing:
- Engine Damage: A bad coil can cause unburned fuel to wash oil off cylinder walls, leading to wear. I saw this ruin a friend’s engine, costing $2,000 to fix.
- Catalytic Converter Damage: Misfires send raw fuel to the converter, which can overheat and fail. A new converter costs $500–$1,500.
- Poor Performance: Faulty coils make your car sluggish and inefficient. My Chevy lost 2–3 MPG before I replaced a bad coil.
- Stranded Risk: A dead coil can leave you stuck, like when my truck wouldn’t start at the grocery store.
If you suspect a bad coil, don’t wait—test and replace it to avoid bigger problems.
How to Replace Spark Plugs and Ignition Coils
I’ve done this job a dozen times, and it’s straightforward with the right tools. Here’s how I replace both on a coil-on-plug system:
- Gather Tools: You’ll need a ratchet, spark plug socket, extension, torque wrench, dielectric grease, and a coil puller (optional). I spent $50 on a basic tool kit.
- Disconnect the Battery: Unhook the negative terminal to avoid shocks. I forgot this once and got a mild zap.
- Remove the Coils: Unplug the coil’s electrical connector and remove the bolt holding it in place. Pull gently to pop it off. My Chevy’s coils were snug, so I used a puller.
- Replace Spark Plugs: Unscrew the old plugs with a socket and extension. Install new plugs, torqued to your car’s specs (usually 10–20 ft-lbs). I use NGK or Bosch plugs for reliability.
- Install New Coils (If Needed): If replacing coils, plug in the new ones, apply dielectric grease to the boot, and bolt them down. I tighten to about 5–7 ft-lbs.
- Reconnect Everything: Plug in the coils, reconnect the battery, and start the car to check for issues.
- Test Drive: Take a short drive to ensure smooth running. I always check for misfires or warning lights afterward.
It takes me about an hour for a 4-cylinder car, longer for a V6 or V8. If you’re new to this, watch a YouTube video for your car model first.
Tips for DIYers
Here’s what I’ve learned to make the job easier:
- Buy Quality Parts: I stick with OEM or trusted brands like NGK, Bosch, or Denso for plugs and coils. Cheap parts fail faster.
- Keep Records: Note the mileage and date when you replace parts. I use a notebook to track my truck’s maintenance.
- Work Cold: Let the engine cool to avoid burns. I burned my hand once working on a hot engine.
- Check Gaps: Ensure spark plugs are gapped correctly (check your manual). I use a $5 gap tool for precision.
- Label Coils: Mark each coil’s position to avoid mixing them up. I use painter’s tape and a marker.
When to Call a Professional
If you’re not comfortable with DIY, a mechanic can handle this. I’ve taken cars to shops when I didn’t have time or tools. Expect to pay $100–$300 for labor, plus parts. A pro can also diagnose tricky issues, like when my friend’s car had a misfire caused by a bad fuel injector, not the coil or plug.
My Experience with Coils and Plugs
When my Chevy started misfiring at 110,000 miles, I replaced the spark plugs first, thinking they were the issue. The misfire stayed, so I tested the coils and found one was bad. I swapped all six coils since they were original, and the engine ran like new. It cost me $200 for parts, but it saved me from a bigger repair down the road. Since then, I always check coils when doing plugs on high-mileage cars.
Conclusion
Deciding whether to change ignition coils with spark plugs comes down to your car’s condition, mileage, and symptoms. From my years of wrenching, I can tell you it’s not always necessary, but it’s smart to test your coils and replace them if they’re old or failing. A smooth-running engine is worth the effort, and swapping both can save you time and prevent future breakdowns.
If you’re a DIYer like me or heading to a mechanic, keep an eye on misfires, check engine lights, and mileage to make the call. Grab your tools, pop the hood, and keep your ride humming—your car will thank you for it.
Frequently Asked Questions
Should you change ignition coils with spark plugs?
Not always. Replace coils if they’re old (over 100,000 miles), failing, or causing misfires. Test them first to be sure.
How do I know if my ignition coils are bad?
Look for misfires, rough idle, poor fuel economy, hard starting, or a check engine light. Test with a multimeter or scanner.
How long do ignition coils last?
Coils can last 100,000 miles or more, but heat, vibration, or age can cause them to fail sooner.
Can I replace just one ignition coil?
Yes, if only one is bad. I often replace just the faulty coil to save money, but swap all on high-mileage cars.
How much does it cost to replace ignition coils and spark plugs?
Spark plugs cost $5–$25 each, coils $20–$100 each. Labor adds $80–$150 per hour. DIY saves on labor.
Can bad coils damage my engine?
Yes. Faulty coils can cause misfires, leading to unburned fuel damaging the catalytic converter or engine.
How do I test an ignition coil?
Check for cracks, swap coils between cylinders to see if the misfire moves, or use a multimeter to test resistance.
David Peterson, the chief editor of sparepartscare. I am an automobile engineer and assign to an local firm with much experience in automobile equipment. During the time, most of my experience is related to the Industry of cars parts. I learned about the thing, when working with experienced inspectors, one must be as good as the inspector, or better, with knowledge of the project as well as the practical aspects of automobile industry.
