Can New Spark Plugs Be Bad?

Although spark plugs rarely fail and have a pretty wide service interval, when they go, the symptoms are usually pretty severe. Moreover, diagnosing bad spark plug symptoms can also be tricky since the same symptoms will be present if ignition coils or spark plug leads fail. And on top of everything, a new spark plug with a factory defect can lead you in an entirely wrong direction. But we will cover everything here so you can avoid that.

So, can new spark plugs be bad? The answer is yes; like everything man-made, spark plugs can have factory defects causing them to not work at all or work but have poor performance. However, that rarely ever happens, and it’s much more likely that something else is wrong with the engine.

Can New Spark Plugs Be Bad?

Why Would New Spark Plugs Go Bad?

In case your brand-new spark plugs were working when you first installed them but have failed prematurely, chances are it’s not defective spark plugs that caused it. Instead, you should first check if you have bought the correct spark plug type. A spark plug with a bigger gap than needed will wear out quicker and put more strain on other ignition components.

Furthermore, a too-high or too-low spark plug heat rating will lead to contamination much quicker and, ultimately, failure. But if you are certain the spark plug type is correct, then there could be a fault in the ignition coils or spark plug leads. As a matter of fact, the two could have been the cause of whichever symptoms led you to replace the spark plugs in the first place.

And lastly, engine overheating can kill spark plugs very fast by melting the electrodes, which basically wears them out by simulating 30,000 to 40,000 miles of driving. Also, a clogged catalytic converter will cause the same effect since it increases combustion chamber temperatures.

But if overheating is too obvious, you should check if something is messing with the air/fuel ratio. That could be a faulty MAF sensor, O2 sensor, vacuum leaks, low fuel pressure, and clogged or leaking injectors as the most common causes.

How Can You Tell If a Brand New Spark Plug is Bad

The easiest way to tell if a new spark plug is bad is by paying attention to how the engine behaves before you replace them. So, if the engine was running well and there were no fault codes, but it began misfiring after new spark plugs, you can rest assured there is something wrong with the new spark plugs. That’s unless you messed something up when installing them.

But the most bulletproof way of telling if new spark plugs are bad is by scanning the fault codes with an OBD2 reader. For example, let’s say you get a P0303 code which indicates that cylinder number three is misfiring. After that, switch the cylinder number three and number four spark plugs, and if the fault code moves to cylinder number four (P0304), you can know for sure that the spark plug is bad.

However, if you suspect that all spark plugs are bad and you get a random misfire code (P0300), the chances of all spark plugs being bad from the factory are slim to none. The only possible cause, in that case, is that you bought the wrong spark plugs or that something else is wrong with the ignition system.

Can New Spark Plugs Be Bad

So, can brand-new spark pugs be bad? Yes, new spark plugs can absolutely be bad. A lot of repair technicians report getting spark plugs without an electrode, with a cracked porcelain insulator, and there is even one case where the spark plug came without any internals. Without any internal means, the spark plug only had the porcelain insulator and the metal thread but none of the electrodes or ground connections on the inside.

Also, some more subtle damage can happen. For example, the spark plug ground electrode could have been hit during transportation or storage. And since hitting the ground electrode decreases the gap, it can lead to poor performance and misfires.

And I can even say from my experience that spark plugs can be defective. A friend of mine had bought a brand new Italian motorcycle that had developed a misfire early on. Naturally, he didn’t want to take it to the closest dealer, which was hundreds of miles away, so we began our private investigation.

Well, as soon as we tried to take the spark plug out, it broke. The reason was that the electrode inside the porcelain insulator was corroded, and the cause was most likely a defective insulator that let moisture inside. Needless to say, we replaced the spark plug, and the bike never had any misfire issues afterward. And that answers the question of can new spark plugs be bad from first-hand experience.

What To Do If New Spark Plugs Are Bad

If the new spark plugs are bad because of a factory defect and you can prove it, you should return them and get a replacement. No self-respecting auto parts shop will deny a replacement for a defective part, whatever it may be, as long as you have a receipt.

But, whatever the case may be, you will have to replace it; there is no going around that, but luckily, spark plugs are pretty cheap. On the other hand, if the spark plugs were initially working but had failed prematurely, you should have the ignition system inspected to see if something else is faulty, like wiring or ignition coils.

can brand new spark plugs be bad

What To Look Out For When Buying New Spark Plugs

When buying new spark plugs, you should always check what type the manufacturer recommends. Sometimes you can find a sticker in the engine bay with the correct spark plug type, and other times, you might find it in the owner’s manual. But if you can’t, then contact a local dealer, and they will help you. On the other hand, you can ask what type of spark plugs your engine needs on model-specific forums, and you will get the correct answer 99% of the time.

And while we can say that you should pay attention to the spark plug gap, size, heat rating, and material when buying them, all those will be within specification when buying them by your car model. Moreover, spark plug specifications are presented in brand-specific codes, so it can be difficult to figure out what the specifications are.

But you can do a little experimentation with spark plug materials. For example, instead of conventional copper spark plugs, get iridium or platinum ones. Both iridium and platinum new spark plugs cost more but will last significantly longer, bringing the long-term maintenance bill down. However, keep in mind that some engines don’t like those spark plug materials, so ultimately, buying the manufacturer-recommended plugs is the only foolproof option.


Q: Can new spark plugs misfire?

New spark plugs can cause a misfire only if they are defective right from the factory or if you have bought the wrong type of spark plug for your vehicle. However, both scenarios are highly unlikely, which means that something else is causing the misfire, maybe a bad ignition coil or spark plug leads.

Q: Are new spark plugs good?

Yes, new spark plugs are good and can never be bad for the engine. Also, spark plugs are a part of regular maintenance with their own service intervals, which are typically at 20,000 to 50,000 miles, depending on the vehicle.

Q: What happens if I overtighten spark plugs?

Overtightening spark plugs can lead to misfires and detonation because the ceramic insulator can stretch and break. Also, you could strip the cylinder head threads, especially if the cylinder head is aluminum, and that can be a seriously expensive fix. But keep in mind that it’s always best to tighten the spark plugs below the correct torque spec than over it.

Q: What kills spark plugs?

The three main things that kill spark plugs are carbon deposits, lean air-fuel mixture, and engine overheating. A lean air-fuel mixture melts the spark plug electrode, and so does an overheating engine. Carbon deposits and a lean air-fuel mixture are caused by faulty sensors (mainly MAF and O2) and also by a clogged catalytic converter or DPF filter.

Q: How long do new spark plugs last?

The spark plug lifespan depends on the electrode material. Conventional copper spark plugs last between 20,000 and 50,000 miles. On the other hand, platinum spark plugs last between 60,000 and 100,000 miles, while iridium spark plugs can last up to 150,000 miles.

Final Words

Although the answer to the main question is positive, meaning new spark plugs can be bad, the chances of that being the case are slim to none, as said earlier. Yes, spark plugs can be defective from the factory with missing electrodes, internal corrosion, damaged spark plug gaps, etc. But even the most experienced mechanics with 20+ years of experience have only come across something like that maybe once or twice during their entire career.

So, you should check if the new spark plugs are bad because it can happen, but also check if you bought the correct spark plug type or if maybe something else is faulty in the ignition system. Also, if at all possible, find a way to test the new spark plugs or switch them around and see what kind of fault codes the ECU reports.


Ibro Cehic

From a young age, I was captivated by cars and motorcycles, and my first driving experience only fueled my passion further. By the age of thirteen, I was already tinkering with vehicles and knew that my life would revolve around them in some way. Combining this passion with my love for writing, I now share my automotive expertise with fellow enthusiasts through my articles.

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