Bad Spark Plug Symptoms

When was the last time you changed the spark plugs in your car? There are thoughts that you need to do it once every 20 000 to 40 000 miles. But it may differ. Car producers are usually more positive about this. For example, Mazda states in 2016 Mazda 3 maintenance documents that the spark plugs should be changed every 75 000 miles.

The spark plugs producers are careful with recommendations. Guys from NGK say that it all depends on the type of spark plugs you bought and many other things. Let's find out what the symptoms of bad spark plugs are so that you could replace them right in time.

Bad Spark Plug

Symptom 1: Rough idle

Well, there are some other possible reasons for rough idle but quite often spark plugs are to be blamed. If a spark plug fails, there will be pauses in work of a certain cylinder. So the idle will be rough, there might occur some vibrations.

Symptom 2: Poorer performance

It's hard to notice that the engine started performing poorly. The performance deteriorates step by step without sharp changes. But in the end, when spark plugs are awfully worn out, they may lead to a solid drop in car performance. You push the gas pedal and feel no proper acceleration? Consider changing the spark plugs.

Symptom 3: Higher fuel consumption

Worse fuel economy can occur if one spark plug is dead or fails often. In this case some fuel won't be burnt and one cylinder will be out of order. The fuel will just go down to oil pan. At the same time, the engine will have to work without one cylinder and it will burn more fuel to get the same acceleration for you.

Symptom 4: Bad engine start

Spark plugs ignite the fuel in combustion chamber. When the engine is still cold after some downtime, the bad spark plug will be easier to detect. If you notice that the time of rotating the engine with the starter became longer than usual, one of the most obvious reasons is bad spark plug. Although, some other problems may also occur.

Symptom 5: Engine misfires

Misfires can occur on any RPM, but they are usually easily found when the engine is idling. Just open the hood and look at the engine. Also listen to the sounds. Once there is a misfire, you will se a little bump of the engine. It will also sound rough, as if it's going to stall. But it can actually stall if the spark plugs are in awful condition.

Symptom 6: Backfire

Sometimes powerful engines with a modified exhaust system may show backfire if the spark plugs are bad. The fire that comes out of the exhaust pipe may look cool, but it shows bad performance. Some fuel gets into exhaust system instead of being burnt, and it burns in the exhaust pipe.

Symptom 7: Check Engine light

When you see a 'Check Engine' light on, it doesn't necessarily mean huge troubles. Here, our colleagues from Edmunds wrote a big article of how to check why your 'Check Engine' light is on. And one of possible reasons is a bad spark plug. The emission control system may start registering higher emissions and the alarm light starts blinking.

Symptom 8: Spark plug's appearance

If you still hesitate whether you need to change the spark plugs, just unscrew them one by one and look at the working part of electrode.

There are some things that might tell you it's time to change the plugs:

  • oil cover on the electrode part of the plug;
  • soot deposits on the working part of the element;
  • changes in the form of main elements;
  • changes in color comparing to original spark plug;
  • molten elements of the plug.

Symptom 9: Big drop while accelerating hard

When you press the gas pedal hard, you expect to accelerate like crazy. But bad spark plugs won't be able to ignite the rich fuel mixture correctly. In this case you will experience sudden drop in acceleration - it will seem that the engine is going to stall. But after just some moments, the vehicle will start accelerating faster.

Symptom 10: One cylinder is dead

If one cylinder is dead, it may mean that one spark plug doesn't work at all. The usual symptoms are sharp performance loss, poor acceleration, high fuel consumption and bad vibration when idling. Driving the vehicle with one dead cylinder for a long time is not recommended. This can lead to mechanical damages. One dead cylinder will also cause fuel leaks into the oil pan. The oil will then mix with fuel and lose its quality which will result in reducing the engine lifespan.

What else can cause troubles like bad spark plugs?

The majority of the symptoms of bad spark plugs can also occur when other units are broken.

Spark plug wires will create basically the same problems when they are out of order. If you changed the spark plugs recently, but they are broken again, replace the wires. Guys from Autoblog recommend to check and change the spark plug wires once every 30 000 to 40 000 miles. But producers usually recommend the replacement of the wires right when you change your spark plugs.

Ignition coils may also create the same troubles as broken spark plugs. Many cars have the same amount of ignition coils as spark plugs - one coil governs one plug. If the ignition coil is out of order, it will destroy the plug and will send wrong signals. There is no specific mileage of when you should change the ignition coils, but they can usually work well between 100 000 and 120 000 miles.

Poor quality of fuel may also show the same symptoms as bad spark plugs. Moreover, bad fuel can kill spark plugs, too. By poor fuel we understand not only poor quality but also inappropriate fuel for your engine - like type, octane number, and other features.

 

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CarAraC Research

About the authors

The CarAraC research team is composed of seasoned auto mechanics and automotive industry professionals, including individuals with advanced degrees and certifications in their field. Our team members boast prestigious credentials, reflecting their extensive knowledge and skills. These qualifications include: IMI: Institute of the Motor Industry, ASE-Certified Master Automobile Technicians; Coventry University, Graduate of MA in Automotive Journalism; Politecnico di Torino, Italy, MS Automotive Engineering; Ss. Cyril and Methodius University in Skopje, Mechanical University in Skopje; TOC Automotive College; DHA Suffa University, Department of Mechanical Engineering

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REBECCA
18-Jan-2023 (Wed, 09:20)
I have a Chrysler 2006, 300 - V6 it starts and then as I drive it for less than a few minutes the engine stops, and I have a problem stopping it. The battery is 3 years and one month old. Could it be battery since I have a 36-month free replacement period plus 36-month discount period equals 72-month limited warranty? Or would the spark plugs do this?
Dmitry Sapko 19-Jan-2023 Thu, 16:37 It could be alternator, wiring, ECU, software glitch, fuel supply problem, air supply blockage, etc. But very unlikely a battery or plugs.