9 Signs Your Spark Plugs Are Failing

The  Internal Combustion Engine (ICE) is one of the greatest inventions in human history - it revolutionized life and the way humans all over the world would travel for generations to come and these IC  engines are still very much in use in automobiles today. In vehicles with petrol engines, air and fuel are mixed before compression and then an electric spark is used for ignition. 

It is these small, rarely acknowledged, often overlooked spark plugs in Internal Combustion Engines that are responsible for creating that all-important spark of electricity that ignites the air/fuel mixture within the cylinders of your engine (combustion) which is needed to start your vehicle. They emit a bolt of electricity across a short gap which ignites the air/fuel mix that sets the pistons in motion and gets your vehicle moving.

So next time your car won’t start, don’t automatically assume you have a flat battery or that you have run out of petrol, it could just be that your spark plugs have lost their spark. No SPARK, no START! 

What Are The Most Common Signs Of Failing Spark Plugs?

Below are the most common telltale signs and symptoms of fouled or failing spark plugs. Once you familiarise yourself with them it will be a lot easier to address the problems when they appear, long before the spark plugs fail completely.

Let's delve into each of these signs and symptoms and see how failing spark plugs can cause each of them.

• Engine Misfiring

An engine that stumbles or misfires instead of running smoothly can often be attributed to faulty or failing spark plugs. The most common causes of misfires are improperly installed, mishandled or badly worn spark plugs, malfunctioning ignition coils, carbon tracking, faulty spark plug wiring and vacuum leaks (loss of compression). When engines misfire due to faulty spark plugs delaying or interrupting the combustion process, it is known as a  “spark misfire.” A misfire can occur in any of the vehicle's cylinders and simply means that one or more of the cylinders in your engine are not producing the power they should. 

Misfiring motors have to work harder to maintain power, which places a huge burden on fuel economy and can also lead to long-term damage if left unattended. Oftentimes, replacing bad spark plugs will take care of the problem.  

Other reasons engines can misfire:

However, faulty spark plugs are not the sole reason that an engine motor misfires. As we discussed, an internal combustion engine relies on fuel, air and a spark in order to run. If any of these three components are not working in sync, or if the air/fuel mix is incorrect or the fuel is blocked for some reason, a misfire will occur.  

When your engine misfires it feels like the vehicle momentarily loses power or cuts out. Acceleration is sluggish or rough and the car feels like it is jerky, shaking and unbalanced when driving because the cylinders are not firing correctly. This leads to an extremely uncomfortable ride and higher emissions.

• Engine Knocking

If you hear a distinct knocking sound coming from your engine, especially when accelerating, it is typically caused by dirty or worn-out spark plugs. When spark plugs are malfunctioning they tend to not detonate properly and not all of the fuel is ignited during each revolution. This causes unburned fuel to sit in some of the cylinders and eat away at the cylinder walls. Eventually, the fuel and vapour will detonate which causes the knocking sound you hear coming from the engine. 

• Engine Runs At A Rough Idle (Rough Idling)

The idle speed of your car should feel consistent without skipping or slipping. If your car is idling rough, it won't feel smooth, the engine sounds rough and jittery - in fact, your entire vehicle may vibrate. There are many different problems that could result in a rough idle but for the purposes of this article, it would indicate bad or malfunctioning spark plugs. 

Faulty spark plugs can cause delayed sparks which make it more difficult for your engine to idle properly, especially if your car has been sitting for several hours or if you are attempting a cold start (due to condensation in the combustion chamber).

• Difficulty Starting Engine (Hard Start)

When a car engine won’t start, there are a few potential culprits, including a bad ignition, a broken alternator, a dead battery, and one that is often overlooked: defective spark plugs. Without this crucial spark for ignition, you’ll not be going anywhere. 

• Engine Surging And Jerky Ride 

When this happens while driving, it means the engine is not working efficiently, sucking in more air than is needed in the combustion process, which causes continual stop-start motions. Again, this leads to an uncomfortable – and potentially dangerous – ride. 

• Loss Of Acceleration/lack Of Power 

An unresponsive and apathetic accelerator is usually the result of dirty, fouled or weak spark plugs which cannot catch a spark efficiently. This causes the engine to become sluggish. You may want to consider a service or change of spark plugs to get things revved up again. 

• High Fuel Consumption

Failing, loose or dirty spark plugs cause poor fuel economy and can have a negative impact on your fuel mileage. So if you find yourself filling up at the petrol station more than you used to, a cheap spark plug replacement could be all that is needed to get your fuel efficiency back on track. 

• Your Check Engine Light Comes On

If the spark plug wires or the spark plugs themselves are faulty your Check Engine Light could come on. This should never be ignored as this particular problem could lead to a clogged catalytic converter, damaged ignition coils, or issues with your oxygen sensor.

• Black Exhaust Smoke & Higher Emissions

If you notice thick, black smoke coming from the exhaust, it usually indicates that there is another problem in addition to the faulty spark plug and it is best you take the car to a mechanic soonest. 

What Should Your Next Steps Be

If your vehicle is experiencing any of the above mentioned issues and you suspect spark plug failure, a trip to your mechanic for an inspection and or repairs/maintenance is advised. Bear in mind that most problems caused by failing spark plugs are relatively simple and easy to fix if caught in time.

However, continuing to drive with failing or dirty spark plugs will lead to more serious and far more costly problems. These problems can escalate quickly and before you know it you could have massive engine damage and even total engine failure on your hands. Never allow these  symptoms to go unchecked and get to that point.

Common Causes Of Bad Or Failing Spark Plugs 

For optimum vehicle performance, your engine’s spark plugs should be clean with no damage to the electrodes. If your spark plugs become dirty or fouled, or begin to fail, it will affect your engine's performance. A fouled spark plug is one that has become soiled by oil, fuel or carbon or one that is blistered from running too hot. 

The most common causes of bad or failing spark plugs include: regularly driving at slow speeds, clogged air filters, dirty fuel injectors, fuel/air mix being too rich and excessive idling.

If your spark plugs are showing signs of failing, you will need to replace them to avoid costly engine repairs. Generally, it’s better to replace all plugs at the same time to ensure consistent levels of performance. 

Spark Plugs Life-span And Maintenance

Spark plugs do need regular maintenance and replacement which fortunately is relatively cheap and easy. Most vehicle manufacturers recommend getting spark plugs serviced roughly every 30,000 miles. This prevents decay, carbon fouling, worn spark plug tips and issues with the cylinders and combustion chambers. 

Fortunately, spark plugs are designed for long-term durability (between 80,000 - 100,000 miles) but how long they actually last depends on the brand, model and type of spark plug you have chosen, if they have been maintained and serviced regularly and of course, on the vehicle itself. 

Have a look at the average lifespans of different plug types, but bear in mind they might become damaged earlier than expected: 

• A standard copper spark plug - up to 10,000-20,000 miles.

• Silver plugs (older vehicles) - up to 20,000 miles. 

• Expensive iridium/platinum spark plugs - up to 60,000 miles.

• Extended-life/long-life spark plugs - up to 100,000 miles.

• High-end iridium spark plugs - up to 100,000 miles 

• Extended-life iridium spark plug - 120,000 miles.

• Double platinum spark plug - 100,000 miles 
   

Some high-end performance and luxury models may have shorter intervals. The importance of routine maintenance checks cannot be highlighted enough and should include oil changes, air filter replacements, tire rotation and servicing or replacement of SPARK PLUGS.

Replacement Spark Plugs Cost In South Africa

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