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Do I Need To Replace Ignition Coils With Spark Plugs?

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Majority of the vehicles possess internal-combustion engines that need 3 key elements to function, namely — fuel, air and electricity. Ignition coils amplify voltage from your car’s charging system to supply power to the spark plugs. Every spark plug has its very own ignition coil. Like every car component, ignition coils could also fail. Now you may be asking, “Do I need to replace ignition coils with spark plugs?” The answer is, it depends. Are you already seeing signs of coil damage? Then the answer is yes. But if not — then that won't be necessary. In this article we will learn more about the other scenarios that should help you determine if you should have those ignition coils replaced with the spark plugs.

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Do I Need To Replace Ignition Coils With Spark Plugs: The Basics

Before we answer the question “Do I need to replace ignition coils with spark plugs?” — let us first cover the basics to understand things better. First of all, what is an ignition coil? Ignition coils are electrical components on the engine. As mentioned they amplify voltage from the vehicle’s charging system (battery and alternator) and deliver power to the spark plugs. 


Because a vehicle's battery produces a low voltage current that is insufficient to ignite the fuel and start the engine on its own, ignition coils are required. The ignition coils solve this difficulty by converting the battery's low voltage current into a much higher voltage current.

Simply put, ignition coils allow a spark to be produced for the car to start and run.


Coil-on-plug is the most common type in modern vehicles, with one ignition coil directly linked to each spark plug. A central coil pack or individual coils with wires leading to the spark plugs are used in some cars. A smaller number of automobiles have two ignition cassettes, each powering half of the spark plugs, or one coil per two spark plugs.


Although most ignition coils are long-lasting and dependable, a faulty coil can cause under-hood havoc. An automobile cannot run smoothly until high voltage is applied to the spark plugs to ignite the air-fuel mixture. The majority of coil failures are caused by secondary winding problems.


The thin lacquer insulation between the two windings can erode with time. The windings are sometimes no longer shielded from the earth. Heat and vibration are the most common causes of coil difficulties.


Because of faulty windings or improper connections inside the coil, a sudden failure is possible. Hard starting, repeated high-speed misses, or a steady decline in ignition system performance are more common symptoms of coil difficulties.


Coils can be checked with an ohmmeter (most coils will read around 8,000 ohms) or a Sun machine's tiny scope. On the scope, a normal coil produces a “heartbeat” pattern, shorted windings make a “bumpy L” pattern, and open windings form a flat horizontal line.


By placing one probe of a cheap test lamp on the metal container and the other on the primary and high-tension terminals, all coils with metal housings can be checked for grounded windings. The windings are grounded out and the coil is faulty if the tester lights up or you witness sparks.


Many service manuals propose temporarily replacing a suspected bad coil with a known good one. You'll know the original coil was defective if the ignition works properly with the good coil. Coil tower spark leakage or a broken tower can sometimes be repaired, but it's usually advisable to get a new coil.


Are ignition coils the same as spark plugs?


Being able to know if ignition coils are the same as spark plugs will help you understand the answer to, “Do I need to replace ignition coils with spark plugs? While spark plugs and ignition coils are not interchangeable or are not the same – they are both essential components of a vehicle's ignition system or to be more precise, components of a gasoline-powered vehicle's ignition system. Diesel engines do not utilize spark plugs since the fuel ignites through compression rather than a spark.


A spark plug is a device that delivers electric current from an ignition system to the combustion chamber of a spark-ignition engine, allowing an electric spark to ignite the compressed fuel/air mixture while keeping combustion pressure within the engine under control.

Do I Need to Replace Ignition Coils With Spark Plugs:  How often should ignition coils be replaced?


It's critical to understand when an ignition coil needs to be replaced in order to keep your engine operating properly. Normally, an ignition coil on a car should last for at least 100,000 miles. When the coil starts to wear out and loses its ability to transfer power, you'll notice a drop in gas mileage. Because your automobile uses more fuel to run, you will also notice having to spend more money on gas than usual. This is because if your vehicle's ignition coils break down and the spark plugs don't get enough power, your vehicle will adjust by raising its fuel usage.


You will also know that your ignition coil already needs to be replaced when an engine misfires. This happens when one or more engine cylinders are not able to fire properly due to a lack of air, fuel, or in the case of a faulty ignition coil — lack of spark. Misfires usually manifest as a choppy idle, a loss of power or even a loud pounding sound.


Is it OK to replace just one ignition coil?

One coil pack is good for two engine cylinders, and you should just replace the faulty coil pack. There is no way that one faulty coil pack will influence the others. Also, call packs either work or don't work; there is no middle ground. If you merely replace the one that's broken, there's a lower risk that others will soon follow.

It would be a mistake to replace coil packs that are still in good condition and are operating normally. Coil packs that are in good operating order are better and more reliable than fresh new coil packs that have not been tested. You should rely on the known reliability of old ignition coils that are still operating. However, if one pack starts to fail once the odometer reaches roughly 75,000 miles, you should replace all of them.

When one coil pack fails, some service garage may recommend replacing all of them. In that scenario, inquire about the rationale for each change with the mechanics. If it appears logical, follow their advice.

If you do not have enough budget to replace them all, replace the ones that are in a cluster or are extremely difficult to get. A few coil packs, for example, could be found under the air intake plenum on the engine's underside. For removing the coil packs, the service garage can demand a higher labor rate. If one of them is defective, you should replace them all to save money on mechanic services.

Do I Need to Replace Ignition Coils With Spark Plugs: What are signs of a bad engine coil?


Besides the things already mentioned, a defective ignition coil can also hinder a car from starting in some situations. Your vehicle could also not be starting for a variety of reasons, including a dead battery or a defective starter. A specialist can perform a diagnostic test to see if your ignition coils are the source of your engine's poor performance.


If it's time to repair your ignition coils, your check engine light may illuminate. However, this light could come on for a variety of reasons, and a mechanic can evaluate your vehicle to figure out what's wrong.


Another sign that you have a bad engine coil is black smoke from your exhaust pipe. This is not natural and could signal a problem with your ignition coils. Keep a watch out for these warning signals that an ignition coil is deteriorating. It will be easier to identify when to replace coil packs or ignition coils if you are aware of these indicators.


Can I drive with a bad ignition coil?


Before you even start asking, “Do I need to replace ignition coils with spark plugs?” — you may be asking, can I drive with a bad ignition coil? 


A car with one or more malfunctioning ignition coils will be inefficiently powered and run badly, if at all. Additionally, because unspent gasoline makes its way into the exhaust system due to the bad ignition coil, the misfiring engine when being run for an extended period of time can harm the catalytic converters and oxygen sensors.


So if you suspect your ignition coils need to be replaced, you should not drive your vehicle. You certainly can drive the car but then you risk serious engine damage if you continue to operate a car with faulty ignition coils.


The Verdict: Do I Need to Replace Ignition Coils With Spark Plugs?


Ignition coils and spark plugs are inextricably linked. If one fails, the other will be unable to work correctly. So do I need to replace ignition coils with spark plugs? The answer is that it really depends. The most common component to replace in conjunction with the ignition coils is the spark plugs. Spark plugs that have become worn can put undue strain on the coils, and the time it takes to replace both components is typically overlapping.


The spark plugs are the most usual component to change in conjunction with the ignition coils. It's best to replace both components at the same time if your ignition coils have failed due to worn-out spark plugs. However, unless there are symptoms that your ignition coils are deteriorating, it is not required to replace them at the same time as your spark plugs — most especially if you are just replacing the spark plugs as part of normal or routine maintenance.


If the ignition/spark plug wires are old, worn, or damaged, it is advised that they be replaced. If moisture has damaged the ignition coils (for example, due to an oil leak), the source of the moisture should be treated at the same time to prevent the problem from recurring.


If you're having problems with your ignition coil, get in touch with a mechanic immediately. “Do I need to replace ignition coils with spark plugs?” is one of the first questions you should be asking him or her. Allow your mechanic to evaluate your vehicle to see if both your ignition coils and spark plugs need to be replaced.


To at least have an idea how your mechanic will decide to determine if an ignition coil needs to be replaced, what he will be doing is examine the primary and secondary ignition circuits. The mechanic will be using a digital multimeter to check both of these ignition circuits.


Resistance is measured with a digital multimeter. Your mechanic may need to consult your owner's manual to determine the ignition coils' normal resistance range. If the primary or secondary resistances are outside of this range, the coil should be changed.


Special tools and equipment are required to diagnose and replace faulty ignition coils. Even a little error might cause catastrophic damage to the spark plugs and other engine components. As a result, rather than attempting to execute this work on your own, it is advisable to contact a mechanic.


Are ignition coils expensive?


The price of a replacement ignition coil is determined by the vehicle's make and model. Some coils are as low as $75, while others cost upwards of $300. Labor charges will range between $50 and $100 per hour if the replacement is done professionally. You will be spending a few hundred dollars for a basic coil-on-plug system whereas a cassette-style system can go as high as up to $1000. 


The price is determined not only by the coil's style but its difficulty to access as well. It is always advisable to replace the spark plugs as the manufacturer has recommended and immediately address oil leaks when they are still minor, so that any excess wear and damage to the ignition coils can be avoided.


Even if the car is well-maintained, ignition coil failure may eventually be unavoidable due to age. Aftermarket ignition coils are frequently accessible and less priced in this situation, but they can be less reliable than the original equipment that came on the car in some cases.

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