Spark plugs are essential components of any gas-powered engine. Their job is to transmit an electrical signal from the coil to the engine’s cylinder timing, igniting the air-fuel mixture.
How long do spark plugs last? Fortunately, spark plugs do not wear out fast. However, their lifespan does depend on the plug and your driving style. Generally, you can expect to get roughly 80,000 miles out of them before having to replace them. But if you notice one of these symptoms, it is time to look into changing out the spark plugs.
We will now go over the primary symptoms of how to tell if a spark plug is failing. Don’t worry about a lengthy fix, either; all you will need to do is change the spark plugs!
What Makes a Spark Plug Go Bad?
Spark plugs are designed to last, but they don’t last forever. After several months, there are several reasons for a spark plug going bad:
- Wear and Tear: Like anything, spark plugs have continued wear and tear. The plug is constantly exposed to extreme heat and electrical sparking, which will ultimately wear down the electrodes and lessen the effectiveness of the spark.
- Carbon Accumulation: If your engine is running too rich (meaning too much fuel and not enough air mixed together), carbon will accumulate on the spark plug. Carbon buildup insulates the spark plugs and prevents them from firing.
- Oil Controlled or Fouled: If your piston rings or valve guides are worn out and causing oil to breach the combustion chamber, the spark plug will be oil-soaked or fouled. When spark plugs are oil controlled or fouled, they will not ignite the fuel mixture as well. Oil or fouled plugs may cause poor engine performance which is one of the biggest discrepancies in findings for a fouled spark plug.
- Over-Heated: Overheating the spark plug will accelerate electrode wear. Physically incorrect, poor fuel quality, too little fuel supply to the fire and overheating the engine will all accelerate spark plug wear.
- Incorrectly Installed: Correctly installed spark plugs or the wrong spark plug type will fail prematurely. Correctly installed spark plugs longevity of its life.
Having said that, spark plugs supply the power for ignition purposes, therefore, changing the plugs has an impact on your engine performance, fuel efficiency, and emission levels. Identify the signs of a bad spark plug early and change old plugs out before your engine stops working.
Symptoms of Bad Spark Plugs
There is no single symptom that will help you tell if a spark plug is bad. You can have 2 or more symptoms and each one is different. Below are all the symptoms your car can have.
Loss of acceleration
One of the most of is loss of acceleration. This can happen when the efficiency of the spark plug is decreased. It consists of several materials and each one has to be efficient to send the electrical signal to the engine at the right moment.
You will eventually lose this efficiency, meaning the spark plug won’t send a signal at all or it will send it later than it should.
If no signal is sent, the cylinder won’t be efficient, and your car will literally be working on 3 cylinders or less.
Another issue is that the spark plug won’t send the signal at the right time or it will send it at a lower voltage for the cylinder to produce power, that is what we are also referencing in loss of acceleration.
We want to add, this issue can happen due to a bad fuel injector, a camshaft, or crankshaft sensor, or possibly a clogged fuel filter.
It is a good idea to start by replacing the spark plugs, especially so if they are old. Sometimes you will most likely have to replace the spark plug wires too.
High fuel consumption
This is a common symptom usually related to a malfunctioning spark plug. Why?
When the spark plug is negatively affected, its efficiency is decreased, and it will not combust the fuel/air mixture properly. Your car will require more fuel that directly increases fuel consumption.
The symptom can also occur because of a gap that is either too large or too small between the electrode and central piece on a spark plug.
The gap is set by the manufacturer and measured in millimeters. Cars have a different gap so you will need a tool to measure that and adjust it. You can also replace the spark plug.
Engine Misfires
This is the most common issue with a car’s wiring. Misfire simply means the mixture of air and fuel in a cylinder won’t ignite at an appropriate time. You will hear the engine literally working erratically and you can hear explosion sound coming out of the exhaust.
A misfire means that the electrical signal from the coil won’t send the correct signal at the correct time to the spark plug, or the sparkplug won’t transfer the electrical signal at the correct time.
An electrical signal can be sent when the piston is going up in the cylinder or when the piston is coming down. Therefore, either way, you will notice poor performance, increased fuel consumption, and poor starting capability.
Keep in mind that if a camshaft sensor or crankshaft sensor is damaged, that can cause a misfire as well. However, if your car has an onboard computer, it will be noted and provided with a code.
Surging Engine
Here we can see a common symptom related to a bad spark plug in in 99% of cases. It is very simple to notice. While driving your car you will notice power loss and performance degradation.
This is from one or more spark plugs not working. When you press the throttle pedal and increase RPM’s a spark plug suddenly starts working. This is what gives your car more power than it had two seconds ago.
This is a common symptom in spark plugs that are failing. At some RPMs, they “turn off” but when the electrical signal rate increases at a higher RPM a spark plug will start to fire.
Yes, this is not something you want to feel in your car and it is not safe for you or other vehicles. This could lead to an accident, or you may damage the engine.
Rough Idling
When your engine idles, it should be smooth and quiet, which means that all components are functioning as they should. However, if a spark plug fails, you will feel the vibrations and notice the rough idle.
The engine is functioning normally, but with vibrations, the symptom is typical if there is one or more reasons related to the spark plug. The spark plug is not igniting the fuel/air mixture when it should, resulting in vibrations you feel.
This is NOT the same symptom as a misfire, but it can look the same. A misfire is a more serious symptom with more damaging effects, you want to take care of this symptom if you experience it.
This is a small symptom of an issue but it does show you that some of your spark plugs are functioning correctly.
Hard starts
If starting your engine is a hard task especially in cold conditions, look to replace your spark plugs.
We should note that this symptom is one of the first to emerge and this does not mean that your spark plug is dead, it means that your spark plug or plugs are dying and not transmitting the electrical signal to light the spark plug up as they should.
This is the first symptom of a more complex problem ahead. Your car will continue to have problems starting and eventually the engine will not even start.
Regardless, it is always a good idea to check to see if spark plugs and wires are functioning well. After replacing spark plugs, the difference in starting will be significant.
You may be thinking about what bad spark plugs look like. The most common sign is a damaged curved part, or damaged electrode, or a carbon composite. You can see that the inside space around the electrode is clogged and the overall spark plug is dirty.
And don’t forget that an engine that “consumes” oil due to damaged piston rings or rubber seals on valves will damage spark plugs over time quicker than in a correctly running engine.
Oil doesn’t burn as coal as gasoline does and this necessarily composites will affect the electrodes of spark plugs.
Black Exhaust Smoke
Black, thick exhaust smoke can also be caused by bad spark plugs, which may further increase carbon emissions. When this symptom of bad spark plugs occurs, it’s best to take your vehicle into a mechanic or your local auto service center, as it’s likely that the problem is multi-layered (the catalytic converter may be involved, for example).
Conclusion
You now have an understanding of how to tell if a spark plug is bad. Whatever symptom you do have, or however many symptoms you have, you will need to check and replace the spark plugs. In many cases, it will be as easy as it was mentioned above and your car will now work properly again.
Just remember that spark plugs are the tiniest part of your car with a whole lot of power, it is no wonder why spending a little extra money on some high-end units is worth it. They will last longer and reduce the possibility of any of these symptoms occurring.