How To Diagnose Spark Plug Problems?


Spark plugs are tiny components that fit inside your engine. Despite their size, they’re critical to the combustion process inside the engine’s chambers. When spark plugs don’t work correctly, the engine struggles to generate power reliably and smoothly.

You can diagnose spark plugs by understanding their everyday issues and the symptoms that come with them. For instance, problematic spark plugs will cause engine misfiring, reduced fuel efficiency, difficulty starting, and acceleration problems. In some cases, inspecting and cleaning those spark plugs will solve the situation in the short term. However, replacing them is best when they’re extensively damaged or worn out.

This guide will help you understand the common problems that spark plugs experience. Then, you’ll discover what symptoms to look out for and what you can do to fix the problem.

How Do You Diagnose Common Spark Plug Problems?

The most direct way to diagnose spark plug problems is to remove the ones in your engine and inspect them up close, looking for signs of wear and damage. 

Of course, constantly doing that won’t be practical for most people.

You can diagnose the most common spark plug problems by paying attention to your car’s performance. Spark plugs that aren’t in excellent condition will display many symptoms you can look out for, even without lifting your car hood.

Here are some of the most common spark plug problems and how to deal with them:

Engine Misfiring

The problem: The first common problem with spark plugs is engine misfiring. A misfire happens when the combustion process in an engine chamber is incomplete or doesn’t happen at all. Seeing as how a combustion engine has many combustions happening continuously, misfiring is very problematic.

Engine misfiring happens because one or more spark plugs are worn out. That’s because a worn-out spark plug fails to produce the high-voltage sparks necessary to fully ignite the fuel and air mixture inside the combustion chamber.

The signs: Engine misfiring caused by worn-out spark plugs will display many signs. The most basic sign is that the Check Engine light will illuminate on your dashboard.

However, a more tell-tale sign is that the engine shakes and shudders instead of running smoothly. Whether the car is idling or mobile, the worn-out spark plug prevents the engine from combusting air and fuel continuously.

The solution: There are two solutions to this problem. The first is to clean the spark plugs if it’s not extensively damaged. This is a short-term solution that might work in some cases.

However, severely worn-out spark plugs must be replaced with new ones as they can’t function correctly anymore.

Read: Denso vs NGK – Which Spark Plugs Should You Use?

Reduced Fuel Efficiency

The problem: Another way to diagnose spark plug problems is to pay attention to your vehicle’s fuel consumption. That’s because problematic spark plugs will cause your engine to burn much more fuel than it should.

When spark plugs become damaged or worn out, they’ll struggle to produce the sparks necessary for combustion. The engine’s computer will compensate for that by mistakenly sending more fuel into the chambers, which reduces the vehicle’s overall fuel efficiency.

The signs: This spark plug problem can be pretty subtle because the symptoms only appear in the long term. So, pay attention to how much fuel your car uses.

If you find yourself at the gas station filling your tank more often than usual, that could indicate that you have spark plug problems.

The solution: If a drop in fuel efficiency is the only symptom, your spark plugs likely only have minor damage or wear. So, you should remove and inspect them up close.

Cleaning them and ensuring they can produce sparks normally will be enough to get them working correctly and restore your car’s fuel efficiency.

Read: Why Is There Oil On My Spark Plug Threads?

Difficulty Starting

The problem: You can also tell that your spark plugs are experiencing problems when the engine struggles to start. Under normal conditions, a car engine will crank and start in about 1-2 seconds. However, taking much longer than that means it’s struggling to get the combustion process started.

The severity of this problem will depend on the condition of your spark plugs. If the problem is minor, they’ll only cause a delay in the engine cranking and starting.

However, severely worn-out or damaged plugs will prevent your engine from starting at all.

The signs: The symptoms are pretty clear and straightforward for this spark plug problem. 

When you turn the key in your ignition, the engine will take far too long to crank and start. That is, of course, if the engine starts at all.

Another way to confirm that the spark plugs are to blame is to check your car battery and starter. Suppose those two components are in excellent working condition, yet the engine has difficulty starting. In that case, it’s clearly a problem with the spark plugs.

The solution: If your spark plugs are at a point where starting the engine becomes too challenging for them, you’re better off replacing them immediately.

Doing so will save you plenty of time and stress from dealing with the problems they’ll create, as they’re likely approaching the end of their usefulness.

Read: 5 Ways to Improve Poor Fuel Economy of Your Car

Rough Accelerating And Surging

The problem: Some spark plug problems aren’t apparent until they’re under stress, like when accelerating your vehicle. 

Accelerating will normally cause spark plugs to deliver more substantial and frequent sparks. However, spark plugs in excellent condition will have no problems coping with the sudden demand for stronger sparks to help the engine generate more power.

However, problematic spark plugs might not be able to cope with the increased demand. So, despite the increased air and fuel entering the engine, the spark plugs can’t combust the mixture fast enough to keep up with the increased demand for sparks.

The signs: These spark plug problems will become apparent when accelerating your vehicle. The engine will struggle to ignite the air and fuel inside quickly enough to keep up with the acceleration.

So, from behind the wheel, you’ll experience this as rough acceleration, surging, and delayed acceleration. Overall, it’ll seem like your engine is working much harder than it usually would, and you’ll find it unresponsive as you press down on your gas pedal.

The solution: If you only experience these spark plug problem symptoms when accelerating, it likely means that the spark plugs are only partially damaged or worn out.

So, you must take them out to better understand their actual condition.

Some spark plugs can be saved with a thorough cleaning. Those will continue to work normally until the end of their expected lifespan.

However, spark plugs that are too far gone must be replaced with new ones. The ones you have can no longer perform under heavy loads (e.g. when the engine is accelerating), so they’ll be unreliable when you need them the most.

Read: What Happens if You Put Diesel in a Gas Car?

Final Thoughts

Spark plugs are small but crucial components in your car’s engine. Sure, the engine can still start and run despite having dirty or worn-out spark plugs. However, that engine will struggle to operate smoothly as a result.

So, always ensure that you check and clean your spark plugs regularly. Most people do that as part of their regular maintenance schedule, alongside things like oil changes.

However, you should preemptively replace your spark plugs when you know they’re approaching the end of their lifespan. That’ll save you plenty of stress as you’ll avoid the problems listed above.

Read: EGR Delete Explained (Pros & Cons)

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