Is your car misfiring? Do you have difficulty starting the engine? These are just a couple of the signs that you have a faulty coil pack. What’s a coil pack you ask? Well, simply put it’s an electronically controlled pack of ignition coils. We’ll discuss all about coil pack in this post. From the symptoms that you have a faulty coil pack to how to test them. Afterward, we’ll also let you know how much you may need to pay for a replacement.
- What’s a coil pack?
- Types of ignition coils
- Testing the coil pack
- Replacement costs
What’s a Coil Pack?
As mentioned, a coil pack is a pack of ignition coils. It replaces the role of the distributor coil present in older cars and is electronically controlled by the car’s computer to create a spark for each spark plug in an engine cylinder. The coil pack takes voltage from your car’s battery and builds up as much as 50,000 to 70,000 volts which it then transfers to the spark plug via the spark plug cables.
The spark then ignites the fuel and air mixture inside of your engine’s cylinders, starting the combustion process. Put it simply, it transfers electricity from your battery to create a spark and start your combustion process.
Unless you have a diesel engine, the ignition coil is essential for your engine’s operation. If it were to go bad, your car won’t run properly or won’t even start. A diesel engine on the other hand simply relies on its high compression within the cylinders to start the combustion process, eliminating the need for spark plugs and ignition coils. This is part of the reason why diesel engines often run more reliably, as they don’t need ignition coils and spark plugs to run. So if you have a diesel car, you can rest easy.
You can learn more about ignition systems in the video below:
Types of Ignition Coils
We will be focusing on the coil pack in this post. However, there are different types of ignition coils and we think it’ll be good for you to know about them since your vehicle might use a different type of ignition coil.
Can-Type Ignition Coil and Distributor Coil
If your car was made before 1990, chances are this is the type of coil that you have. Called can-type because of their cylindrical shape, the can-type ignition coil connects to your spark plugs and transfers electricity via high voltage or HT cables and the distributor. Older versions would have been filled with oil which acts as an insulator and a coolant. However, most of them have a dry insulation design.
Can-type is largely similar to distributor coils as they distribute the high voltage power from one coil to all the spark plugs. In principle, distributor coils are similar to can-type as they both distribute high voltage power from one coil to multiple spark plugs. The difference is that in a distributor coil they are mechanically driven.
Ignition Block Coil
An ignition block is somewhat similar to distributor-type coils since they sit remotely from the engine. However, instead of having just one coil, they have several ignition coils inside them depending on how many the car needs. They are then connected by HT cables to each spark plug.
Ignition blocks are available with either a single or dual spark technology. A single-spark ignition block would supply each cylinder with high voltage electricity. Meanwhile, in a dual-spark block, the high voltage electricity is fed simultaneously to two cylinders. In this case, one of the cylinders has to be on the “power stroke” and the other on the “exhaust stroke”.
Pencil or Coil-On-Plug Ignition Coil and Coil Packs
The previously-mentioned type of coils normally sits remotely from the engine. On the other hand, a pencil or coil-on-plug ignition coil sits on top of the spark plug, hence the coil-on-plug name. It’s also often called a pencil coil because of the shape that resembles a pencil.
Anyway, since they sit right on top of the spark plugs, they can feed the voltage straight into the plugs, which minimizes power loss. They are used in vehicles with an electronic ignition system, and much like the ignition block coil, they are available as either single-spark or dual-spark coils. Most modern cars would use this type of coil as it’s more efficient.
Meanwhile, a coil pack system is simply a collection of coil-on-plugs housed together in one component, hence the name “coil pack”. They’re also often known as “rail”. The rail is placed across a bank of spark plugs, and they work the same way as a coil-on-plug system. The only difference being they are housed within one component.
As mentioned, your vehicle may use a different type of ignition coil than coil packs. Find out which type it uses in the owner’s manual, as this will affect how to test and replace them should they go bad. We wrote a great article on ignition coils and you can learn more about them here.
Symptoms of a Faulty Coil Pack
An engine misfire is when one or more of the engine’s cylinders isn’t firing, hence called a misfire. Because one or more cylinders isn’t firing, the engine won’t produce as much power and it will feel like your engine missed a beat. A faulty coil pack can cause this because it’s not supplying power to one or more of the spark plugs. When a spark plug isn’t getting the power it needs, it won’t create a spark and the fuel and air mixture within that cylinder won’t combust.
A misfiring engine is different from a backfiring engine. A backfire is when the fuel and air mixture combusts outside of the engine’s cylinders. A backfiring engine will sound like there’s a small explosion happening in the engine. This is also a serious problem as it can result in serious damage.
Note that the coil pack may not be the cause of a misfiring engine. Other possible causes include faulty spark plugs, bad ignition timing, and loss of engine compression amongst other reasons. Learn more about misfiring engines here.
Rough Idling and Stalling Engine
A misfiring engine will run rougher than usual even when it’s idling. If the problem is severe, a faulty coil pack may lead to a stalling engine. As mentioned, a coil pack supplies power to the spark plug so it can ignite the fuel and air mixture inside the engine. When the coil pack isn’t sending power or sending irregular spark, it will disrupt this combustion process and cause your engine to stall.
Difficulty Starting the Engine
Since the coil pack is part of the ignition system, a faulty coil pack can cause difficulties when starting the engine. This is because a faulty coil pack will send irregular power to the spark plugs, this will then disrupt the engine’s combustion process. When you crank the engine and the spark plugs aren’t firing correctly, the car will have difficulty starting.
If the engine cranks as normal but doesn’t turn on as quickly as it normally does (i.e. you have to turn the key longer than usual), you’re likely looking at an ignition problem. This can either stem from the coil pack, the spark plugs, or the spark plug cables if you have a distributor-type coil.
Check Engine Light
Not all of us are keen drivers and you might miss the symptoms above, and that’s alright. Not everyone is a car enthusiast. That’s why cars have check engine lights. The check engine light is a warning light on your dashboard that lights up when there’s a problem with the engine.
We’ll briefly explain the system: your car has tons of sensors that feed information to the car’s powertrain control module. When the module detects a problem or an irregularity, it will make adjustments to the engine to rectify the issue. When it can’t fix the problem on its own, the module will register an error code and send it to the On-Board Diagnostic system and will then light up the check engine light. This light is basically your car’s way of telling you that something isn’t right. If you see a check engine light, you can use an OBD scanner to see what the problem is.
Not all problems in the car will trigger the check engine light, but a faulty coil pack can trigger this. If you see a check engine light, you should use an OBD scanner to find out what the problem is. If there’s a P0300 error code, this means there’s a cylinder misfire. You won’t know if the coil pack is causing this until you test the coil itself, but now you know what triggered the check engine light in the first place.
Learn more about the check engine light and what you should do if you see them here.
How Long Do Coil Packs Last?
Unlike distributor coils, coil packs have no mechanical component, making them more reliable. While a distributor coil typically lasts for about 30,000 miles, a coil pack usually lasts for around 100,000 miles. So it will be a good while until you have to worry about replacing it. But if it’s been 100,000 miles since you change your coil pack, or you’re seeing the symptoms above, then you need to check your coil pack.
If your coil pack is failing but you’re sure it’s still well under the 100,000-mile mark, there are some things that can cause the coil to fail prematurely. These causes include extreme temperature and weather, moisture, or wiring problems. If your coil pack is failing prematurely, check if your engine is running at a higher than normal temperature. If your engine still uses HT cables, try replacing them with a new one as a bad HT cable can also damage your ignition coils.
How to Test a Coil Pack
As mentioned, a coil pack is a collection of pencil coils or coil-on-plugs that are housed together in one component. To test them, you will need to take out the coil pack, remove the coils, and then test each one of them. But before you do that, remember to prep your car for work:
- Let your engine cool down if you’ve been driving it.
- Park the car in a cool and dry area. You’ll be working with electrical components so make sure your working space is dry and free from moisture.
- Disconnect the negative cable from the battery’s negative terminal.
- Make sure you have a multimeter or a spark tester to test the coils.
- Remove the connectors from the coil pack. Label them if necessary, as they have to be connected to the correct coil for the car to run properly.
- Once the connectors are off, pull out the coil packs with your hand. Be sure to apply even pressure to the front and back of the coil so you don’t bend them, just in case you can still use them.
Once you prep the car and got the tools sorted out, you can begin testing your coil pack. Keep in mind that it may be trickier in some cars to remove the coil pack due to their placement. You will encounter this problem if you have a car with a boxer engine such as Subarus and Porsches. Check with your owner’s manual on how to remove the coil pack properly. There are two ways to check a coil pack: a winding test and a spark test.
Testing the Coil Pack: Winding Test or Ohm Resistance Reading
An ignition coil has two separate coils wrapped around each other, called the primary and secondary winding. Over time, these windings can short out or become open which causes it to go bad. While not the most accurate way to test your coils, you can still tell (to a degree) if your coil has gone bad. To do this method, you will need an Ohm multimeter such as the INNOVA 3320 Auto-Ranging Digital Multimeter. Here’s how to test it out:
- Check your owner’s manual (or online) to see your car’s correct resistance reading for both primary and secondary windings. This varies between cars.
- Connect the multimeter’s positive and negative cable to the terminals. Different coils will have different touch-points for this, depending on how the coil is designed. Be sure to check with your manual or seek online information to find out which pins to attach to.
- Check the readings on the multimeter and compare them to your vehicle’s specifications.
A zero reading means that the coil has shortened internally. While a high reading above the specification means the coil is open. The test can be inaccurate because you can’t test the coil while it’s under load or while the car is running. However, this is still a good test to determine if there’s a problem with the coil. The bottom line is if the reading isn’t what it’s supposed to be, then you may need to change the coil.
Here’s a video on how to test your coil’s windings:
Testing the Coil Pack: Spark Test
The spark test is probably the most accurate way to determine if you have a faulty coil. Even with a faulty ignition coil, your vehicle can sometimes still run just fine. It’s usually when the vehicle is under load – such as when accelerating – that you start to notice the symptoms. The winding test can also be inaccurate as you can’t simulate the load or measure the coil during a car’s operation.
As a result, the surefire way to check is to see if your coils are still generating enough spark for your engine to operate. However, before you do a spark test, keep in mind that you will be testing the coils while your car is running. So, be sure to follow safety procedures religiously. To conduct this test, you will need a spark tester. The OEMTOOLS In-Line Tester should do the trick, or you can use the Lisle Coil on Spark Plug tester if your car has a coil-on-plug system. Here’s how to test them:
- Remove the ignition coil you want to check and plug in the tester.
- Connect the ground wire to the engine.
- Start the engine and see if there’s a strong spark on the tester.
- Repeat the process on the other coils.
Here’s a video from RockAuto Auto Parts on how to do a spark test with your ignition coil:
Coil Pack Replacement Cost
As with any other car part, the replacement cost will depend on your vehicle’s make and model. But in general, a set of coil packs will set you back around $150 – $300. Add labor cost of around $100 – $150 to the equation and the service bill can be as high as $450 for a coil pack replacement.
Of course, some cars may cost more than this. For example, cars with bigger engines and more cylinders such as a six-cylinder or a V8 engine will cost more, since more ignition coils are needed for the engine. Meanwhile, cars with boxer engines may cost you more in labor. This is because their coil pack sits on the side of the engine rather than at the top, making the replacement process more difficult and often time-consuming.
Saving Cost: DIY Coil Pack Replacement
Thankfully, replacing the coil packs in most cars is a pretty easy job. It’s a moderate difficulty repair job at the very most. Here’s what you need to do:
- Disconnect the negative battery terminal from the cable. Make sure you’re working in a dry environment.
- Remove the plastic cover on top of the engine if there is any. You may need a socket wrench to do so as some plastic covers are held down with bolts.
- Disconnect the connectors or cables from the coil packs and label them if necessary so you don’t mix them up.
- Remove the coil from the engine. Some engines may require you to remove a bolt, but otherwise, you can simply pop them out with your hands.
- While you’re at it, consider replacing the spark plugs as well. They usually need to be replaced every 20,000 miles. If you’re replacing the spark plugs, then you need to remove them with a socket wrench.
- Gap the spark plugs to the manufacturer’s specification, then reinsert them into the spark plug socket. You may need a torque wrench and tighten it to your manufacturer’s specification. You should be able to find this in your owner’s manual.
- Install the new coil packs and then reconnect them to the connectors or HT cables.
- Reconnect your car’s negative battery terminal.
- Turn on your car and see if it runs smoothly.
- If your check engine light is on and it won’t go away, check out our guide on how to reset a check engine light.
Keep in mind that the steps may differ depending on your vehicle’s make and model, but that’s the general guide on how to replace the coil pack and spark plugs. If you need a visual guide, check out this video from ECS Tuning:
Your vehicle’s coil pack plays an important role because it’s responsible for powering the spark plugs and it’s essential for the combustion process. A faulty coil pack will disrupt this process as it won’t be able to send the right electrical current. As a result, your engine will misfire and it won’t run as smoothly as it should.
A faulty coil pack is generally a minor problem and is a relatively easy fix. However, it can cause further damage in the long run as it interrupts the engine’s operation. In the long run, it may cause damage to the air intake system, the head gasket, and even the catalytic converter as the misfires can affect engine temperatures and emissions.
If you have a bad coil pack, it’s a good idea to replace them as soon as possible. They can cost as high as $450 but should be a lot less in most cars. Even if it’s still a bit steep, you can save some money by replacing them yourself as you won’t have to pay for labor costs. This can save you as much as $150! Hopefully, this post has helped you learn more about coil packs as well as how to replace them if yours have gone bad.
These tools have been tried and tested by our team, they are ideal for fixing your car at home.