What Happens If Spark Plug Gap is Too Big? Shocking Truth Inside!

You’re driving along and suddenly feel your engine shaking or not picking up speed like it should. That happened to me too. The problem? A spark plug gap that was too big. It’s a small detail, but it can cause big trouble for your engine. If the gap is too wide, your engine may misfire, lose power, waste fuel, or even stall. In this article, I’ll show you how this tiny gap can cause huge problems and what you should do about it.

Engine Misfires More Often

When the spark plug gap is too big, the spark has to travel a longer distance. If the spark can’t jump that wide gap easily, your engine might misfire. That means the fuel in the cylinder doesn’t burn the right way or not at all. Misfiring causes your engine to shake, run rough, or even make a “pop” sound.

I once had a car that would jerk every time I pressed the gas. After checking everything else, I found out the spark plugs had gaps that were too wide. The car misfired constantly because the spark wasn’t strong enough to jump across the large gap, especially at low speeds. It felt like the engine was skipping a beat. This made the ride rough and uncomfortable.

Misfires can also make your car use more fuel than normal. Since some of the fuel doesn’t burn, it gets wasted. You’ll also smell fuel from the exhaust. If misfiring continues, it can hurt the catalytic converter, which is expensive to fix.

The engine control unit (ECU) might also get confused. It can’t figure out the correct air-fuel mix if cylinders keep misfiring. So, your car might lose power, run slow, or stop altogether.

If the weather is cold or if the engine is cold, a bigger gap makes it even harder for the spark to happen. This means misfiring happens more often during winter or in the morning.

• Spark can’t jump the large gap easily.
• Engine may misfire often and shake.
• Unburned fuel wastes gas and hurts performance.
• You may hear popping sounds or smell fuel.
• The ECU struggles to adjust properly.

Loss of Engine Power

Another big thing you’ll notice when the spark plug gap is too wide is that your engine feels weak. It doesn’t respond the same when you hit the gas pedal. That’s because a bigger gap means the spark is weaker or happens late, so the engine doesn’t produce enough power.

I remember once trying to go uphill, and my car just wouldn’t climb properly. It felt like the engine was tired. After some tests, I found the plugs had large gaps. After fixing the gaps, the car climbed the same hill easily. That’s how important this small thing is.

Your engine needs a powerful spark to burn the air-fuel mix completely. When the spark is late or weak, only part of the fuel burns. This makes the engine slow and lazy. Acceleration becomes harder. Even simple tasks like merging onto a highway or overtaking another car become risky because the power isn’t there.

Also, automatic cars may shift gears at the wrong times if the engine isn’t performing well. That leads to jerky movement or a feeling like the car is hesitating before it speeds up.

Sometimes, the engine will knock or ping due to the incomplete burn. This noise isn’t just annoying—it can damage parts over time.

Fixing the gap makes the spark stronger and more accurate, and your car will feel alive again.

• Weak spark causes low power.
• Car struggles during acceleration.
• Driving feels slow, especially uphill.
• Engine may knock or ping.
• Automatic shifting feels weird.

Poor Fuel Economy

If your spark plugs have too wide a gap, they waste fuel. This is because the spark doesn’t always ignite all the fuel inside the engine. That unburned fuel goes out the exhaust, meaning you’re paying for fuel you’re not using.

In my case, I noticed I had to fill up the gas tank more often than before. I thought maybe my driving had changed. But after checking the engine, I saw the spark plug gaps were way too big. Once I fixed that, my car started giving me much better mileage again.

Here’s how it works: Your engine burns fuel to create energy. But if the spark doesn’t work well, some of the fuel stays unburned. The oxygen sensor reads this and tells the ECU to add even more fuel. So it becomes a cycle of burning too much fuel for little power.

The engine might also take longer to warm up, which means it uses more fuel during cold starts. And in stop-and-go traffic, you’ll notice the fuel gauge dropping quickly.

A wide gap can also trigger the check engine light. Sometimes, a mechanic might tell you it’s a fuel system issue, but it’s actually a spark plug issue.

Even if the engine runs, it isn’t running at its best. You pay more at the pump and still get poor performance.

• Incomplete burning causes fuel waste.
• Fuel economy drops quickly.
• Engine uses more fuel during cold starts.
• ECU keeps adding more fuel unnecessarily.
• Check engine light may come on.

Hard Starting and Rough Idling

Another thing that happens with a big spark plug gap is that your car becomes hard to start. You may turn the key or push the button, but the engine doesn’t start right away. Sometimes it cranks for a while or even stalls right after starting.

This happened to me during winter. My car wouldn’t start easily in the mornings. After checking the battery and fuel, I finally looked at the spark plugs. The gaps were too wide, so the spark couldn’t jump well when the engine was cold. After closing the gap to the correct size, the car started perfectly every time.

When the spark can’t jump properly, especially in cold or damp weather, it’s very hard for the engine to get going. Even after it starts, the engine might shake or idle unevenly. That’s called rough idling. It feels like the car might die while sitting at a red light or when parked.

Wide gaps also mean weak sparks at low engine speeds, like when you first start the car or let it idle. The engine doesn’t run smooth and makes unusual sounds or vibrations.

You may also smell fuel near the tailpipe after starting. That’s the unburned fuel coming out.

• Car cranks longer or won’t start.
• Rough idle feels shaky or uneven.
• Worse in cold weather or mornings.
• Weak spark can’t ignite cold air-fuel mix.
• Unburned fuel smells after startup.

Spark Plug and Coil Wear Increases

When the spark plug gap is too big, the ignition system has to work harder. That includes the spark plugs and ignition coils. The extra stress causes them to wear out faster than normal.

In my own car, I noticed I had to change spark plugs more often than usual. My mechanic told me the coil was also starting to fail. After checking, we saw the spark plug gaps were much wider than recommended. So both the plugs and coils had been under pressure the whole time.

The ignition coil creates the high voltage needed for the spark. A wide gap means it must generate even higher voltage, which it wasn’t designed for. Over time, this burns out the coil and shortens its life.

The spark plugs get burned tips and may even crack if the spark is too weak or delayed. That also causes carbon buildup, which blocks the spark completely.

Replacing coils and plugs costs more money. And if left unchecked, the damaged parts can cause more serious engine issues.

It’s always cheaper to check and fix the gap early than to replace worn-out parts later.

• Coils and plugs work harder with wide gaps.
• Early wear leads to higher repair costs.
• Cracked plugs and burnt tips appear.
• Carbon builds up faster.
• Coils can fail due to high voltage demand.

Engine Damage Over Time

If a spark plug gap is too wide for a long time, it can cause damage to the engine. This is because of repeated misfires, unburned fuel, and poor combustion. All these problems slowly eat away at your engine’s health.

I had a friend who ignored his engine misfiring for months. He thought it was just a small issue. Later, his catalytic converter failed because it was clogged with unburned fuel. That repair cost him over a thousand dollars.

Misfiring causes heat and vibration in parts that should stay cool and balanced. The pistons, valves, and cylinder walls all get affected. Over time, this can lead to oil leaks, loss of compression, and even engine failure.

Unburned fuel in the exhaust also damages the oxygen sensor and catalytic converter. These parts are expensive and critical to emissions control.

Even if you don’t feel the damage right away, your engine is slowly suffering from too much stress. It becomes less reliable and more costly to maintain.

Fixing a spark plug gap might take just a few minutes, but it saves you thousands in repairs later.

• Misfires cause long-term engine damage.
• Heat and vibration hurt pistons and valves.
• Catalytic converter can fail from unburned fuel.
• Oxygen sensors wear out faster.
• Engine reliability and lifespan reduce.

Final Thoughts

A small spark plug gap mistake can turn into a big engine problem. If the gap is too wide, it can cause misfires, low power, wasted fuel, rough idling, and even engine damage over time. Luckily, this issue is easy to check and fix. Always check your spark plug gap during maintenance. Doing so keeps your engine running smooth, saves you money, and gives you better performance every time you drive.

Frequently Asked Questions (FAQs)

Is it bad to drive with a wide spark plug gap?

Yes, it is bad to drive with a spark plug gap that is too wide. A wide gap weakens the spark, making it harder to ignite the air-fuel mixture in your engine. This causes misfires, poor fuel efficiency, and engine hesitation. Over time, it can damage other engine parts like the ignition coil and catalytic converter. Even if the car still runs, it doesn’t run well. You’ll feel less power and might waste more fuel. It’s best to fix the gap as soon as you notice a problem.

Can a wide spark plug gap cause a check engine light?

Yes, a wide spark plug gap can cause your check engine light to come on. When the gap is too big, the spark might not fire properly, which leads to misfires. Your engine’s computer detects this misfire and stores an error code. This can trigger the check engine light. Sometimes it shows as a cylinder misfire code. If this keeps happening, it can damage the oxygen sensors and catalytic converter, making the problem worse. A simple gap check can save you from big repairs and annoying warning lights.

Do I need special tools to check the spark plug gap?

You don’t need expensive tools, but you do need a spark plug gap tool. These tools are cheap and available at auto parts stores. The tool has measurements that let you check the gap size easily. Some tools are round disks; others are like feeler gauges. You use it to see how big the gap is and then gently bend the ground strap to make it smaller or bigger. Always do this carefully to avoid breaking the spark plug. No fancy equipment is needed, just patience and the right gap tool.

Is it okay to use spark plugs right out of the box?

It depends on the type of spark plug. Some modern plugs come pre-gapped and ready to install, especially iridium or platinum ones. But even then, it’s a good idea to check the gap before installing them. During shipping, the gap might have changed slightly. If the gap is too wide or too small, it will affect how your engine runs. So, even if the box says “pre-gapped,” it’s smart to double-check before you put them in your engine. It can save you from future problems.

Can changing the spark plug gap fix engine problems?

Yes, fixing the spark plug gap can solve many engine issues like misfiring, rough idling, and poor fuel economy. If the gap is too wide, your engine may not perform well. By adjusting the gap to the correct size, you help the spark ignite the fuel better, which leads to smoother performance and better mileage. It’s a simple fix that can make a big difference. However, if your spark plugs are already damaged, it’s best to replace them instead of just adjusting the gap.

Do I need to gap iridium spark plugs?

Most iridium spark plugs come pre-gapped from the factory and are not meant to be adjusted. They have very thin tips, and trying to gap them can damage the delicate electrode. But it’s still a good idea to double-check the gap using a proper tool. If the gap is way off, it might have been dropped or bent during shipping. If you must adjust them, do it very gently and carefully. But in most cases, iridium plugs don’t need gap adjustments unless your vehicle’s manual says otherwise.

Can bad spark plug gaps lower my car’s mileage?

Yes, spark plugs with the wrong gap can lower your car’s mileage a lot. A big gap means a weak spark, which leads to incomplete combustion. This wastes fuel and makes your engine work harder. Your fuel gauge drops faster, and you have to refuel more often. Many people don’t realize that their mileage problem is because of spark plugs. Simply checking and fixing the gap can bring your mileage back up and help your engine run more efficiently.

Do I have to gap new spark plugs for every car?

Yes, you should check the spark plug gap every time you install new ones, even if they are new. Different cars need different gap sizes based on engine design. The factory setting might not be right for your car’s engine. Always look in your vehicle’s manual to find the correct gap size, and adjust the spark plug accordingly before installing. This small step makes a big difference in performance, mileage, and engine health.