Spark Plug Condition: How To Diagnose Engine Issues

What Are Spark Plugs?

A spark plug is a device that is designed to transmit an electrical signal to the engine, in order to ignite the mixture of air and fuel. Without a working spark plug, your car wouldn’t be able to start up if it runs on petrol/gasoline. The plugs are located within the cylinder heads in the engine and they are controlled by the engine control unit (ECU) via spark plug leads, also known as HT leads and ignition leads.

It’s really important that they are working properly because if they are faulty, you are going to encounter all kinds of mechanical problems. For example, if your spark plug gap (between the two electrodes) is too wide, it can affect the strength of your ignition spark.

Whilst it may seem that all spark plugs are the same, the type that you have in your vehicle depends on the brand of the car. Also, the amount you have is dependant on your engine, for example, a V6 engine will contain 6 plugs, whilst a V12 one will contain 12.

Now that we are more familiar with the workings of a plug, let’s take a closer look at what a good and bad spark plug means for your car. Also, we will discuss how you can diagnose engine problems by assessing the condition of your plugs, and when you may need a spark plug replacement.

How Long Do Spark Plugs Last?

Usually, they need to be replaced every 30,000 – 50,000 miles, however, it is really important that they are regularly checked for faults. You don’t want to end up on the motorway with a broken-down car because of a damaged spark plug!

How long one lasts is highly dependent on the model/make of your vehicle. Getting your plugs checked on annual service is recommended, as it’s beneficial to get your mechanic to check them over for any wear and tear. The sooner these issues are diagnosed, the healthier the engine will be.

Furthermore, another factor to consider is what type of plugs you have. For example, some are designed to have a longer life, such as iridium or platinum plugs, whilst copper ones usually have a shorter life. If you are guilty of putting your foot down on the gas a bit too much, you could add additional wear to your spark plug and in turn, you’ll be coughing up more to get them replaced on a more frequent basis.

Bad Spark Plug Symptoms/When to Check Your Spark Plug

It might be difficult to know when you need to check your spark plugs, after all, we all lose track of time and sometimes we don’t keep up to date with our regular checks. If you’re guilty of lacking in your maintenance schedule, you may want to keep a look out for the following symptoms that will indicate when you need to check them out.

Poor/Slow acceleration
If you have noticed that your vehicle accelerates slowly, this could be due to a worn out plug. This is because the plug becomes less effective in its role of creating an electric spark strong enough to ignite the compressed air and fuel mixture, which in turn results in poor acceleration.

Poor Fuel Efficiency
When a spark plug is faulty, your car might guzzle up petrol way faster than it should. If you notice that you’re putting in petrol way more than you used to, it might be worth checking out your plug. A mechanic would usually check the gap between the spark plug electrodes, and readjust them in necessary.

Rough Sounds When Stationary
If your vehicle is making jittering, rough/loud noises whilst stationary, there may be some faults with your spark plug. On top of rough idling, the car will also vibrate, so make sure you check them out to make sure that the cylinders are not misfiring.

Hard To Start
If you can’t start your car on the first try, before work or the school run, there might be a fault with a worn spark plug.

Misfiring Engine
There could be a fault with the ignition system if your engine keeps misfiring, however, it could also indicate that the ignition lead on the spark plug could be damaged. You’ll hear sputtering sounds coming from the engine and it will have trouble starting. If the engines misfire continues, this could result in lower engine power and a decrease in fuel economy.

Surging/Hesitating Engine
A spark plug problem could be causing the car to hesitate when accelerating or slow down and then suddenly speed up when driving. This could be because there is too much air being taken in by the engine during the combustion process, and therefore there is a delay in the power being delivered.

The Different Conditions Of A Spark Plug

Healthy
A healthy spark plug is one that looks reasonably clean, but it’s okay if there is a small number of deposits on it. One end is small and tapered, where the spark plug lead connects to it. The other end looks like a bulb shape with a small metal rod coming out of the middle, and a hook to one side. The middle rod is the electrode which passes the electricity to the engine.

Covered In Oil
If your spark plug has oil on it, it may indicate that you have an oil leak, and it will need to be changed more regularly because of contamination issues. You will also need to replace the brown seal. Furthermore, you will need to investigate and rectify the oil leak.

Soaked
A soaked plug can mean that there is engine flooding, which occurs when you try to start the engine up multiple times without it actually starting. An option is to remove the spark plugs, clean and then refit them.

Burned
Burnt spark plugs will look blistered, they will have melted electrodes, or have white-ish deposits on them. This is a sign that they are running at very high temperatures and this can often be due to an overheated engine. Also, some other causes of this could be loose plugs, plugs becoming too lean/susceptible to air/fuel mixture and they need to be replaced and the ignition timing for the plugs is off.

Worn or Broken Electrodes
A worn, rusty or eroded plug most definitely needs to be replaced, as it has exceeded its lifespan. If it is broken, it might mean that your car has the wrong kind of spark plug in it. Check the owners manual to see what kind is the correct one for you, or have a mechanic check it out for you. Having the wrong kind will cause extensive engine damage, so this is really important.

Carbon Fouled
Carbon fouled plugs have black, dry soot covering them. This is usually caused by a filthy air filter, often driving your vehicle too slow, the fuel/air mixture is too rich or staying stationary for too long. If this is the issue, it is recommended that a professional assess your vehicle and provide a recommendation for more suitable spark plugs to replace the damaged ones.

What Do These Conditions Tell You About Your Engine?

If your spark plugs are in any of the conditions outlined above, it is essential that you get your engine looked at by a mechanic. You can tell if something is wrong with your engine by the way your spark plugs look when they are checked over. Most symptoms indicated by your spark plug condition are easy to fix, and examining them for a quick diagnostic provides you with a good idea of how well your engine is performing. Worn, burned, oiled, or damaged spark plugs indicate a problem with your engine.

Spark Plug Replacement Near Me

If you would like to install new spark plugs yourself, we have provided a guide for you on how to do so: How To: Fit New Spark Plugs. However, if you don’t feel confident and would prefer to have it done professionally, Sinspeed is the place to go. We are based in Greenwich, London and we offer a large range of services. We can replace your spark plugs, diagnose any engine problems and provide the necessary repairs. So don’t delay, either call us to book an appointment or fill in our easy online form!