Spark plugs ignite fuel in your internal combustion engine, so if they don’t work as required, the engine will fail to deliver the needed power and torque. Fouled spark plugs are one of the common problems with the ignition system that is relatively easy to solve. But you need to understand the reasons for this to prevent the problem from happening again after you replace the fouled spark plugs.
In short, a fouled spark plug is a contaminated plug that fails to ignite the fuel properly. This happens because of carbon buildup, oil, or fuel contamination. This leads to improper spark formation and the fuel is not ignited in the combustion chamber leading to other critical problems with your engine and its components.
In this article, I will cover the following:
- When is a spark plug considered fouled?
- What happens when a spark plug is fouled?
- What are the most common reasons for the fouled spark plugs?
- Solving the problem of the fouled spark plugs?
- Can you drive when the spark plugs are fouled?
Common criteria of when a spark plug is considered fouled
Usually, you will take the wrench and unscrew the spark plug to look at it in those cases only when there is some problem with how the engine works. But suddenly you see that some parts of the spark plug are wet or covered in some kind of black buildup. What’s this? Is the spark plug fouled?
Here’s how you can check this:
- the spark plug is fouled when the firing tip insulator is contaminated and covered in something like oil or carbon buildup;
- also, the metal tip of the plug may be contaminated heavily which prevents the spark plug from producing the correct spark;
- when the contamination embraces the entire end of the plug, bad things may happen like the voltage will go up the plug and not to the metal tip;
- this will make the firing tip produce the spark between the tip itself and the metal body of the plug;
- in such case, the spark plug will not ignite the fuel at all or will ignite it just every other time the cylinder should fire;
- the most common contaminants are carbon buildup and oil – it’s not that hard to distinguish between them.
Also, fouled plug may or may not be wet. If it’s wet, it means that it doesn’t ignite the fuel and the fuel that still gets into the combustion chamber keeps covering it making things even worse. If it’s wet, it means that sometimes this plug fires and ignites the fuel. But it doesn’t mean that the fouled plug still works well.
So, you can easily locate the fouled plug just by looking at it. The metal tip of the spark plug and the insulator of the firing tip should be clean or at least relatively clean. If the insulator is black or covered in oil, this means that the spark plug is not working.
What are the symptoms of the fouled spark plug?
Among the symptoms of the fouled spark plug, I can outline the following ones:
- Engine misfiring. It means that the engine will work quite harshly, lose some power, and may throw an error code that will trigger the check engine light. After reading the code, you may also know which cylinder misfires.
- Gas mileage goes down. The fuel consumption becomes much worse and you just waste the fuel when you drive.
- Emission control systems go mad. Also, the ECU may show other codes from O2 sensors, catalytic converters, EGR valves, and other equipment that overheats and is at risk of being damaged.
- Unstable RPM when idling. The fouled spark plug may lead to spikes and drops in RPM when your vehicle is idling. One cylinder will just turn off spontaneously from time to time.
- Poor engine start. You may need to crank the engine much longer than usual to start it successfully. This may also make the problem of the fouled spark plug worse.
- Dying ignition coils. The fouled spark plug may send the current back to the ignition coil and eventually kill it. After you replace the coil, the bad plug may kill the new coil quite soon, too.
- Knocking engine. When your engine misfires and the fuel is unburnt, the leftovers of the fuel may explode in different parts of the exhaust system and the engine itself. This may lead to engine knocking.
These are the primary symptoms that one or several of your spark plugs are fouled. These symptoms may be combined in different ways, so you won’t encounter them altogether, in most cases. But if you see at least several of these symptoms in your vehicle, it will be quite wise to check the spark plugs.
Unfortunately, such a simple thing as a bad spark plug can eventually lead to fatal engine failures and cause very expensive problems like catalytic converter death, engine oil dilution, poor lubrication, overheating, and eventually fatal damage to the engine. This doesn’t happen quickly but may occur if the problem is ignored.
Reasons for a fouled spark plug
The most obvious reasons for the fouled spark plug in your car are as follows:
- Oil leaks because of bad valve seals or piston rings – the oil contaminates the spark plug heavily.
- Poor quality of fuel – this leads to quick contamination of the plugs with all kinds of buildups.
- Bad or old spark plugs – after some time, the plugs just stop doing their job.
- Faulty ignition coils – when ignition coils don’t activate spark plugs, they don’t fire and are covered with different kinds of buildups.
- Low compression – the fuel won’t burn in low compression, so the problem will develop quickly.
- Damaged spark plug – cracked, broken, or defective spark plugs won’t ignite fuel correctly and will be contaminated quickly.
- Slow driving or short-distance driving – if you always drive the car for short distances, the spark plugs may not heat enough to deal with the natural buildup.
When you understand the most obvious reasons that can lead to spark plug contamination, you obviously get a better understanding of what you can do to solve the problem. As a rule, it’s not hard to locate the issue and set a plan for how you can repair the engine. But in some cases, you will need professional help.
What are the consequences of the fouled spark plug?
While there are almost no short-term consequences of this problem, the condition of your engine may deteriorate heavily if you ignore the problem and keep driving. I don’t recommend driving your car if you notice that some of the symptoms listed above are present in your vehicle.
Here’s what may happen with the car:
- Ignition coil may go bad. This is not a fatal problem but it will make you spend much more money on repair than just if you needed to replace the faulty spark plug.
- Catalytic converter may overheat and even die. When highly overheated, the converter may start literally falling apart. Its ceramic filter may crack and be destroyed which will prevent your car from passing the next emission test.
- The car may lose power and stall. I mentioned this when telling you about the symptoms, but you should understand that sudden stalling and heavy hesitation are also safety issues and they may lead to accidents.
- Fuel explosions (detonation) may cause more issues. Actually, in an old engine, this may lead to fatal failures. Bad detonation may even cause immediate engine death, in some cases.
- Oil dilution and bad lubrication. Some parts of fuel that are not burnt may leak into the cylinder block and eventually dilute the oil. This will lead to bad lubrication and engine damage because of this.
Most of the effects are not short-term problems. So, if you see the check engine light and other symptoms of the fouled spark plug, it doesn’t mean that you have to stop your vehicle, turn off the engine and never start it until you change the spark plug. No, you can drive further but just don’t ignore the problem and check the spark plugs as soon as you can.
How can you solve the problem with fouled spark plugs?
Solving the problems with fouled spark plugs may be as easy as just replacing the bad unit. But it depends on the reason for this problem. For example, if the bad coil or low compression is the culprit in your case, you will not be able to solve the problem just by changing the plug.
I should say first that cleaning the spark plug most likely won’t be a good and long-lasting solution.
Here’s how you may try to deal with the issue:
- use the OBD2 scanner if you have one and check the codes – this may help you understand which cylinder misfires;
- take the ignition coils off the plugs – don’t mix them up when you put them back again;
- unscrew each plug and inspect it – if it has white isolation of the firing tip and is dry and clean, the spark plug is most likely OK;
- if you find a black spark plug with some buildup or contaminant on it, you’ve just found the reason for your problems;
- change the plug and see if the problem disappears (you may also try to swap plugs in different cylinders to see if the error code changes;
- if replacing the plug doesn’t help, you may try to swap ignition coils and see if the error code changes;
- if nothing helps, I recommend going to a specialist.
You can also measure the compression in the engine, check the converter, analyze the ECU with the scanner, check the ignition timing, etc. But for all of these procedures, you will need special tools and experience.
You better address this problem without ignoring it for too long. If you drive several hundred miles with this issue, many other problems may show up.