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Bad or fouled plugs can cause a range of issues for your engine. Check your spark plugs regularly to avoid these issues and use this article as a guide to identify the symptoms of bad and fouled spark plugs.
- Overview
- Difficulty starting your vehicle
- Rough idling
- Engine misfiring
- Lack of acceleration
- Reduced gas mileage
- Lit “Check Engine” light
- Excessive wear or residue on the spark plug
Has your vehicle’s performance suddenly had a drastic change? Engine sputtering or not even running at all? Before you spend money on a mechanic, see if a bad spark plug could be the culprit—and replacing one is a repair you can do on your own. There’s no one sure sign that you have a bad spark plug, so we’ve gathered all the common symptoms in one place so it’s easy to diagnose the problem. Keep reading to see if a simple spark plug swap can keep your vehicle and engine at their peak performance.
Having trouble starting your vehicle is one of the main signs of a bad spark plug.
Listen for rattling, sputtering, or metallic pings that signal when a spark plug is making your engine misfire.
Check if your gas mileage has gotten worse since a bad spark plug won’t burn fuel as efficiently.
Take out your spark plugs to check if the electrodes are worn down or covered in residue.
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Old plugs can’t create a big enough spark to start your ignition.
If your spark plugs are overheating or worn out, the current they produce isn’t strong enough to ignite the fuel that starts your engine. As you turn your key in the ignition, listen for a sputtering noise and notice if it takes a few seconds longer than normal for your engine to roll over.
If you hear a clicking or chattering sound when you try starting your vehicle, then you’re dealing with a battery issue.
by cleaning the terminals or replacing it.
If you only hear a single click or nothing at all when you start your vehicle, then there’s an issue with your vehicle’s starter.
to ensure it’s causing the issue.
A rattling engine is a sign that the spark plug isn’t igniting fuel properly.
Start your vehicle’s engine and let it run. Listen to the engine to see if you hear any rattles, metallic pings, or sputtering rather than a smooth, even sound. An old or fouled spark plug won’t burn fuel completely, so your engine will start vibrating or making unpleasant noises.
Sometimes, the ignition coil that your spark plug sits can cause rough idling.
and compare the readings to your vehicle’s requirements in the manual. If the readings are off, then
Your engine may act sluggish or surge if the spark plug is faulty.
As a spark plug gets older or wears out, it may not produce a spark at all. Since your engine isn’t burning fuel properly, your engine may go through cycles where it isn’t as responsive or it runs harder than it normally would.
Look for signs that your engine is misfiring
, like if it’s vibrating suddenly, making pings or sputtering noises, or stalling.
It takes longer to speed up if your spark plug isn't working properly.
Even if you firmly press on the gas pedal, your vehicle may hesitate if you have a fouled spark plug. Since the old spark plug isn’t burning the fuel properly, your engine won’t be able to keep up and accelerate smoothly.
Your vehicle won’t use fuel as efficiently with a bad spark plug.
When your spark plug doesn’t burn fuel, it doesn’t provide as much power to your engine, which will make your vehicle use more gas. If you notice that your fuel efficiency drops by 3 miles per gallon (0.78 L/km) or more, then there’s a good chance that your spark plugs are misfiring.
If your car doesn’t display it, you can
calculate your vehicle’s fuel consumption
The light will come on if your spark plug causes misfires.
Your “Check Engine” light can come on for a variety of issues, so it may not necessarily mean the spark plug is the issue.
into the link connector port near the left side of your steering column to determine if the spark plug is your issue.
Common engine codes for misfires and spark plugs are P0-300 through P0-308.
Fouled spark plugs may not be able to produce a spark.
Locate your spark plugs by finding where the thick black cables attach to your engine cylinders.
from your engine one at a time using a
, and visually inspect them.
Look for signs of damage
, like a rounded electrode or worn-down insulation in the middle of the cylinder. If you see any issues, then it’s time to
Feb 12, 2023 · If the Check Engine Light is flashing, the spark plugs may be bad. Defective plugs can also lead to a misfiring engine, a rough idle, trouble accelerating, a hard-starting engine, decreased fuel economy and exhaust that smells like fuel. Here are the symptoms that matter the most. 1. Flashing Check Engine Light.
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- Slow acceleration. The most common cause of poor acceleration in most vehicles is a problem in the ignition system. Today's modern engines have multiple sensors that tell the onboard computer and ignition system when to send electric pulses to fire the spark plug, so the issue may be with a faulty sensor.
- Poor Fuel Economy. A fully-functioning spark plug helps burn fuel efficiently in the combustion cycle. When this occurs, your car can achieve better-than-average fuel economy.
- Engine is Misfiring. If the engine misfires, it's typically due to an issue in the ignition system. In modern cars, it's usually due to a sensor malfunction.
- Engine Surging or Hesitating. You may notice the engine hesitating while accelerating. In this case, the engine is not responding correctly to the driver.
- Visual Inspection. Remove and compare your old spark plugs to a new one. If the tip and/or electrode show excessive wear they should be replaced. Also, look for fuel and oil contamination.
- Trouble Starting. If you are experiencing what seems to be longer cranking times, especially on a cold morning, you’ll want to look at your spark plugs and related ignition and fuel system components.
- Rough Idling. If your vehicle’s engine is running rough or noisy when idling, you likely have a problem in your ignition system. Heavy rumbling when waiting at a stoplight or in a drive-thru may indicate your car is overdue for maintenance.
- Misfiring. Misfires are hard to miss, as the engine will shake so badly that you’ll feel the vibration throughout the car. Misfiring results in poor performance, reduced fuel economy, increased emissions, and rough idling.
This video is about How to Identify a Fouled Spark Plug - NGK:https://www.denniskirk.com/ngk
- 2 min
- 1.3M
- Dennis Kirk, Inc.
Dec 19, 2023 · If you’re dealing with a bad spark plug, you’ll likely experience rough idling, which may include rattling noises, excessive vibrations, and sudden surges or drops in the internal combustion engine’s RPM.
