Why Your Car Runs Worse After Changing Spark Plugs? [Typical Reasons]

Have you ever tried changing the spark plugs in your car and wondered why it ran worse than before? Your car is a complex machine that relies on many different parts working together.

Spark plugs are among the most important things in an automobile engine, providing an ignition source for combustion to take place.

In this article, you’ll learn why your car runs worse after changing spark plugs and what may cause such trouble on its own.

Why Your Car Runs Worse After Changing Spark Plugs?

Your car needs to be maintained to run at its best efficiency. The age of your spark plugs can impact your vehicle’s performance.

If you’ve recently replaced your spark plugs and noticed that your car is not running well, don’t worry. There are a couple of things that may be the cause.

Improper Gap

Spark plugs rely on the right spark gap to ensure that each cylinder fires at the precise moment. When the gap is too large, it can lead to misfiring or even damaged parts.

On the other hand, when the gap is too small, there may not be enough power for starting and running and setting off a chain of problems.

Wrong Spark Plug Type or Model

One sign of a worn spark plug is that it won’t always fire your engine. A good spark plug needs to produce a flame and explosive combustion of air and fuel to start your engine.

Ensure that you install the right size for your spark plugs, as installing the wrong size can cause extensive damage. Over time your spark plugs could wear, and you may want to replace them before it gets worse.

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Wrong Torque

Many engines can’t run properly without spark plugs torqued to the proper specification. Torque specs are crucial to properly seat the plug into your engine’s cylinder head.

A torque that’s too little can result in a loose spark plug, which could fall out and cause nasty damage to something else in your engine in the process.

Damaged or Broken Spark Plug Wire

Spark plug wires are an essential component of most engines. The plug wires can easily be damaged, especially when over tightened. Spark plug wires should be replaced as they age and degrade, leading to a performance problem.

Only Replaced One Spark Plug

Most people believe that it’s either too much work or too expensive to replace all the spark plugs in an engine at once. Without replacing all the spark plugs, your engine will lack power, increasing fuel consumption.

Spark Plug Wire Miswired

A miswired spark plug wire will never make your car run right. If you’ve ever installed a new set of spark plugs in your car and noticed that it doesn’t start or run properly, chances are the wires have reversed polarity, and one is miswired.

It should connect the firing lead from the distributor to the plug wire connected to the end of one of the coils with a dot on it, and this will fire the spark plugin that cylinder – and only that cylinder.

Consequences of Wrong Spark Plug Replacement

Spark plugs tend to be among the more complex car parts. Replacing it is an important process to consider for every car owner.

It ensures that you’ll get better gas mileage, but it also improves engine performance and helps protect your engine from various dangers.

1. Rough Idle

While most drivers are familiar with “idling,” many don’t understand what it means. Idling is a term used to describe the process of your vehicle running without moving.

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A rough idle may not seem that dire, but it can signify a serious problem developing within your vehicle’s engine.

As with any problem, the first thing to do is figure out exactly what’s happening. Sometimes irregular idling is a sign of an engine issue, and other times it’s caused by problems elsewhere in the vehicle.

Your car’s engine idling will vary based on your vehicle type. However, some common causes are:

2. Torque

Torque measures rotational force, and spark plugs are turned in with the specified torque. If you don’t tighten the plugs to the correct torque, they can be easily damaged or even break off when you remove them later on.

The plugs must be installed in the engine with the proper torque. Note that if the torque is too low, the plugs may come loose due to combustion gas leakage or vibration, potentially damaging the engine and the plugs.

In contrast, if the torque is too high, the crimping between the insulator and the housing may become loose, compromising the seal’s integrity or breaking the mounting screw thread.

3. Engine Misfire

An engine misfire is when one of your cylinders isn’t firing correctly. The cylinders are where your car’s power comes from.

They compress a mixture of fuel and air to produce a small explosion that moves a piston inside your cylinder, which powers your wheels.

When just one cylinder is misfiring, you might not even notice. But if multiple cylinders are misfiring, you’ll notice and feel it in the form of rough idling and decreased performance.

You may also notice shaking or hear a rattling from under your hood and a decrease in fuel economy.

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Frequently Asked Questions (FAQs):

Will replacing spark plugs stop a misfire?

If you’re having problems with misfires, your spark plugs could be worn out or dirty. Issues include rough idling, poor fuel economy, and acceleration.

You may also notice a decrease in horsepower when accelerating from low speeds. If you experience any of these, it’s time to replace your spark plugs.

Is a torque wrench required for spark plugs?

It’s not required. However, if you want to ensure that your spark plugs are tightened down properly, you can use a torque wrench.

Don’t overtighten to prevent damaging the threads in the block, and don’t under tighten to prevent plugs from firing. Be careful when using a torque wrench to tighten spark plugs because they can easily snap off inside the hole.

What could go wrong when changing spark plugs?

Changing spark plugs can be tricky because there are many factors to consider. It might seem simple, but it’s not.

The wrong spark plugs can cause significant damage to your engine. If the electrode protrudes too far, it can strike the piston.

If it’s too short, it can cause misfires. You might also install the wrong plug. If the thread doesn’t match perfectly, it can damage the threads in the cylinder head, become cross-threaded, or seized.

Are iridium spark plugs better than copper ones?

It depends. Copper spark plugs are old because car manufacturers have used them to ignite an engine’s mixture of air and fuel for many decades.

In contrast, iridium spark plugs are a bit newer than the more traditional copper ones, and they provide automotive enthusiasts with another option.

Do you need to tune your car after changing spark plugs?

Changing spark plugs improves your engine’s performance and efficiency. So, if you have replaced your spark plugs recently, yes, you will need a tune-up. In addition, this can help your car run better and more efficiently.

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Can new spark plugs cause rough idle?

A new spark plug wire can immediately cause an idle problem, but how does it do that? Generally, a new spark plug wire can create a short on the ignition coil or wires. The vehicle will not start or run right.

To diagnose a rough idle problem caused by a new spark plug wire, see your owner’s manual for checking the coil resistance or voltage.

What are the indicators of a bad spark plug?  

Spark plugs themselves are fairly simple little devices. They are used to ignite a fuel-air mixture at the right time in the combustion process – one of the most important parts of automotive engine operation.

A bad spark plug will not allow the vehicle to start or run properly, and it could potentially cause damage to the engine. The signs of a bad spark plug are usually hard to miss for car engines. These are some factors that dictate why spark plugs fail.

  • High fuel consumption
  • Lack of power and acceleration
  • Trouble starting your engine
  • Misfiring of engine

What are spark plug wires?

If you own a vehicle, you’ll know that spark plug wires are essential to your car’s ignition system. Spark plug wires are electrical components.

They transmit electricity from the battery to the spark plugs. A relay delivers power to each spark plug wire. Spark plug wires transfer a charge between the spark plug and the ignition coil. Most engines use two of them, and they may be single, double, or triple leads.

Can spark plug wires be interchangeable?

Spark plug wires are not interchangeable. These wires are a vital component of your vehicle’s engine.

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Each wire differs by its resistance, which affects the heat of the spark to ignite the fuel mixture. If the heat is too high or too low, the spark can’t ignite properly, and your vehicle won’t run efficiently.

Will old spark plugs result in rough idle?

If you have a harsh idle, you could have some old spark plugs to blame. One common issue that results from old spark plugs is a rough idle.

If you hear a loud exhaust rattle when you first start the car, along with a rough idle, then it’s likely that your spark plugs had burnt out and resulted in your recent problems.

Doing It Right

Hopefully, this article taught you why your car runs worse after changing spark plugs. Spark plugs are not a thing to be afraid of, they are just a part of your engine, and if you know how to change spark plugs, you can save hundreds of dollars over the life of your car.

It can be a daunting task for someone who hasn’t done it before, but you can do this with the process.

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