Last Updated: May 2026 Reviewed by: John, ASE-Certified Master Technician at Kwik Kar Auto Dallas Reading time: 8 minutes
A car that struggles to start on a cold Dallas morning or stumbles along when you press the accelerator can all be traced back to a spark plug gone wrong.
Spark plugs hardly get the attention they deserve in routine auto care, despite providing the initial spark to get your engine up and running. It’s only when you begin to experience bad spark plug symptoms that you actually feel the need to go for spark plug replacement.
In this blog, we will tell you everything you need to know about this small yet essential car component, what spark plugs do, and how often you need to change them to keep your vehicle running smoothly.
ASE-certified Kwik Kar Auto Dallas technician replacing spark plugs on a Ford F-150 engine
What are Spark Plugs and What are They Used For?
A Spark plug is a small plug consisting of a layered metal shell with an electrode in the centre. Generally 2-3 inches in length, they are fitted into the cylinder head at the top of the engine.
When a car is turned on, they bring the electrode into contact with the ground strap, which generates a powerful spark. The air-fuel mixture in the combustion engine is thereby ignited, converting the fuel into kinetic energy that drives the vehicle forward.
How Do Spark Plugs Work?
Now, let’s cover the part of what spark plugs do that makes them so vital to your engine performance. When the start function is turned on, the ignition coils boost the incoming voltage from the battery to around 20,000–45,000 volts before sending it onward.
This causes a sudden jolt of electricity across a gap between the electrodes of the spark plug.
The spark ignites the air/fuel mixture inside the combustion chamber, leading to controlled combustion that expands the inner gases in the chamber. The build-up of pressure forces the piston down, thereby turning chemical energy into mechanical energy, which is what delivers power to the wheels to move forward.
Close-up of car spark plugs showing electrode and ignition spark
Spark Plug Importance for Engine Performance
You are most likely to feel Spark Plug importance when they get clogged or wear down with a deposit build-up on their electrodes.
When that happens, your car demands more voltage to fire up the mixture, straining the ignition coils and causing uneven combustion. This can have a negative impact on your fuel efficiency since the fuel is not burnt properly.
Following car maintenance guidelines can keep your engine in top shape for the long haul by proactively acting on issues.
How Do I Know If My Spark Plugs Are Bad?
Spark plugs are designed to be durable, but several factors come together to contribute to a bad spark plug. It may be due to carbon buildup in your engine when the fuel burns with less oxygen, wear and tear due to constantly fluctuating temperatures, and overheating.
Carbon deposits on spark plugs are often worsened by a failing PCV valve service, so both should be inspected at the same visit.
Look out for these signs to know if your spark plug has gone bad.
1. Your check engine light illuminates
A flashing engine light is the most obvious sign that a spark plug has failed or worn out. This indicates that it is no longer able to ignite the air-fuel mixture, amplifying risks of a misfire or damage to your catalytic converter.
Our engine diagnostics service can pinpoint which cylinder is misfiring and whether spark plugs are the cause.
Is it safe to drive with a misfiring engine?
2. Rough Idling
When your engine misfires, the car vibrates or shakes while emitting a rattling or knocking noise as it stops.
3. Slow Acceleration
A failing spark plug can also make the vehicle unresponsive and move sluggishly as you try to speed up. Since the plug could not deliver an intense spark as required, your engine doesn’t have the power to speed up the car as quickly as it would normally do.
4. Poor Gas Mileage
A well-functioning plug ensures that the fuel burns efficiently so that there is less wastage. A plug that has reached its tipping point will eventually affect your gas mileage as it can no longer burn to its full potential.
This will increase your fuel consumption, and you’ll be spending more on getting engine refills.
The U.S. Department of Energy recommends regular maintenance checks for worn components like spark plugs as one of the fuel efficiency tips to reduce unnecessary energy loss.
Copper vs. Platinum vs. Iridium Spark Plugs — What’s the Difference?
Spark plugs aren’t all the same, even though they are designed to perform a similar function. Spark plugs generally come in three major types, each suited for different vehicle types and mileage preferences.
Copper plugs: These are the standard type, consisting of a solid copper core insulated by a durable nickel-alloy electrode. The electrodes wear down faster and thus need to be replaced every 20,000–40,000 miles.
Platinum plugs: Due to a higher melting point, these plugs are better at withstanding heat and can go as far as 100,000 miles.
Iridium spark plugs: Considered to be the highest quality option, they are well known for their superior conduction potential and can last up to 60,000 to 100,000 miles.
How Often to Change Spark Plugs
Spark plugs don’t last forever; they are prone to wearing out quite quickly. So, it’s only fair to ask how long they actually last. Most car makers say you should swap them out around 10,000 miles, but honestly, that varies depending on your car or the spark plug you’re using.
Some need replacing as early as 3,000 to 5,000 miles. It all comes down to the specific make and model, plus the kind of spark plug you’ve got.
Make sure to check the manufacturer’s checklist to learn about the recommended intervals for your particular vehicle. It’s more sensible to err towards the beginning of the replacement window than the end.
Get Your Spark Plugs Replaced at Kwik Kar Auto Dallas
If your vehicle is misfiring, showing a check engine light, or simply due for routine maintenance, our ASE-certified technicians at Kwik Kar Auto Dallas can thoroughly inspect and replace your spark plugs on the go to keep your engine running at peak performance.
We service all makes and models, from Ford F-150s and Chevy Tahoes to Toyota Camrys, without the need for a prior appointment.
Spark plug replacement is part of a full engine tune-up in Dallas; it’s worth combining both services in one visit.
Frequently Asked Questions (FAQs)
Can bad spark plugs damage the engine?
Yes, faulty plugs can wreak havoc with your engine if ignored.
How often should spark plugs be replaced?
It’s recommended to replace spark plugs at the 30,000- and 100,000-mile intervals, but check your owner’s manual and maintenance schedule to know the exact interval for your vehicle. How often you need a replacement also depends on the type of plugs your car requires (e.g., copper, platinum, or iridium) and engine design.
What does a spark plug do in a car?
A faulty or fouled spark plug can stall an engine and prevent it from starting smoothly. A spark plug is a small but critical component that delivers the initial spark to ignite the fuel-air mixture in your engine’s cylinders. The products of the combustion create pressure within the chambers, pushing down the piston that drives the forward motion of the vehicle.
What are the symptoms of a bad spark plug?
When spark plugs go wrong, the car might struggle to start or show rough idling without warning. There is a greater risk of misfires happening, especially under load, while Fuel burning becomes less efficient. As a result, Acceleration feels slow and unresponsive, and the check engine light can be seen blinking.