What Happens If A Spark Plug Gap Is Too Small – Symptoms and Solutions

Every vehicle has a unique spark plug gap specification, which is integral to proper engine performance. Over time, this gap may become too wide as the electrode wears or too small due to a damaged piston.

So what happens if the spark plug gap is too small? This may lead to various engine issues like misfiring if it is smaller than the spec size. In addition, the engine may experience a rough idle. You may also have difficulty starting your vehicle and all this happens because the smaller gap causes the plug to fire at low voltage, delivering a weak spark.

Now, how can you tell if your spark plug gap is way too small? In this article, we will discuss everything there is to know about spark plug gaps being smaller than the recommended size.

What Happens If Spark Plug Gap Is Too Small?

Your vehicle’s engine performance reduces. This is because when the spark plug gap is too small, the plug will fire at a lower voltage. This makes it impossible for the plugs to generate intense sparks capable of igniting the air-fuel mixture.

Spark Plug With Small Gap
Spark Plug With Small Gap

Typically, spark plugs need a voltage of between 12,000 and 25,000 volts or more to properly fire. So, the engine cannot produce maximum power when the spark plugs fire weak sparks at low voltage. As a result, you may experience issues like:

Engine misfiring

When the spark plug gap is too small, some engine cylinders may not produce power, causing engine misfires. This happens because the sparks are not powerful enough to ignite the air/fuel mixture.

Difficulty starting the car

Too small spark plug gaps lead to loss of engine power. Without the proper spark for ignition, you may have trouble starting your car.

Slow acceleration

Due to loss of power from weak sparks, your vehicle may experience slow acceleration. In other words, your car may feel less responsive.

The engine has a rough idle

Sometimes, your car’s engine may sound rough when the plugs fire at low voltage due to a tiny gap. This happens especially when the engine is running at idle.

Read Also : How Long Can You Drive With Bad Spark Plugs : The Effects Of Spark Plug

How Do I Tell My Spark Plug Gap Is Too Small?

The best thing would be to measure the gap and compare it to your car’s spark plug gap specifications. Below are steps to determine if your car’s spark plug is too small.

Step 1: Get a gap tool

There are many tools for measuring the spark plug gap. These include coin-style, blade-style feeler gauge, ramp-style gauge, and wire loop gauge. However, the feeler gauge is the most versatile and effective tool.

Step 2: Check your vehicle’s recommended gap

Each vehicle has specific measurements for the spark plug gap. So, get your car’s owner’s manual and check for the recommended gap size. You could also visit the nearest auto parts store and ask them to help you locate this information.

Step 3: Clean the spark plugs

If you have old spark plugs, clean any dirt you see around the contact points using a wire brush. Removing the dirt build-up will allow you to accurately read your plug’s gap size. However, it would help if you did not use any abrasive cleaner.

But what can you spray in the spark plug hole? You could use a carburetor or brake parts cleaner to dissolve any hardened and tough dirt.

Step 4: Measure the gap

Get your feeler gauge or whichever gap-measuring device you have. Then, choose the recommended gap size on your feeler gauge. Next, place the feeler gauge between the plug’s central electrode tips. If the tool does not fit, the spark plug gap is too small, and you must widen it a little.

Spark plug fouling

A small spark plug gap can cause the spark plug to foul, which means that carbon and other deposits build up on the electrode, reducing its ability to conduct electricity

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Should I Increase the Spark Plug Gap If It Is Too Small?

Yes. If, after measuring the spark plug gap, you find it too small, you must widen it slightly. Then all you need is the feeler gauge to increase the hole. And using this tool, bend the bottom electrode slightly away from the central electrode. The gap should not be too small or too wide.

Accordingly, increasing the spark plug gap also increases the voltage required to jump the gap. Consequently, this helps maximize burn efficiency and better engine performance. It also ensures smooth start-up performance and increased fuel efficiency.

Is There A Standard Gap Size For Spark Plugs?

Most vehicles’ spark plug gap size ranges between 0.028 and 0.060 inches. However, there is no standard gap size as the gap setting differs from one vehicle to another. For example, if you are using your car for racing, the best gap size for most applications is 0.020 to 0.040 inches.

Meanwhile, the NGK spark plugs usually come pre-gapped at 0.044 inches, and you should keep the gap the same when new. But if the gap becomes smaller over time, you must adjust it. Generally, a damaged piston is what causes the spark plug electrode to bend, making it too small.


The spark plug gap is very critical to your vehicle’s engine performance. For instance, when the gap is too small, you may experience many issues, including engine misfires and trouble starting your car.

Nevertheless, don’t worry because you can tell when the gap is too small and widen it using a spark plug gauge tool. The important thing is knowing the correct gap size for your specific vehicle.

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