Have you been noticing frequent misfires or slow starts?
Think it’s a weak battery or a fuel system issue?
Here’s the twist: the real troublemaker can be something much smaller, like an incorrect spark plug gap.
This tiny space between a spark plug’s electrodes significantly affects your engine’s efficiency. If the gap is too small or too big, it can lead to wasted fuel and other performance issues.
To learn more about this essential gap, we’ll dive into what it is, why it matters, and how you can adjust the spark plugs for better combustion.
This Article Contains:
- What Is a Spark Plug Gap and Why Is It Important?
- What Spark Plug Gap Setting Does Your Engine Need?
- How to Gap Spark Plugs Step-By-Step
- What Happens If the Spark Gap Is Too Narrow or Too Wide?
- Should You Inspect Pre-Gapped Plugs?
- How Often Should You Check and Readjust the Spark Plugs?
- 3 FAQs About Spark Plug Gap
What Is a Spark Plug Gap and Why Is It Important?
The spark plug gap is the small space between the center and ground electrode (also called a ground strap, which is a curved piece of steel at the end of the plug).
This is where the spark forms to ignite the air-fuel mixture in your engine. A proper gap is vital for efficient combustion and smooth engine operation. That’s because even a small change in the spark plug gap can weaken or strengthen the spark, affecting your engine’s performance.
So, if you want to check whether your car has the right gap setting, keep reading further.
What Spark Plug Gap Setting Does Your Engine Need?
Whether your car has a big or small engine, here are the ideal gap settings you need to fire up the perfect ignition spark:
- Standard street engine (ignition coil with distributor): 0.025″
- Performance engine (ignition coil with distributor): 0.028″
- Racing car engine (coil-on–plug – COP): 0.016″
- Distributorless ignition system (coil-on-plug – COP): up to 0.060″
So, why does this spark plug gap size vary?
Your engine’s optimal plug gap depends on several factors — it’s not a one-size-fits-all situation. Here’s what you need to consider:
- Fuel type and alcohol concentration: Fuel with a higher alcohol content contains more ethanol (which means it has more oxygen), making the air-fuel mixture leaner than gasoline. To ignite this lean mixture, your engine needs a narrow gap for efficient combustion, or else it won’t combust.
- Cylinder pressure at spark discharge: High compression or forced induction engines, like turbochargers or superchargers, operate under higher pressures when the spark fires. This means they need more voltage to create a spark and perform better with a narrow gap. Meanwhile, naturally aspirated engines tend to perform better with a slightly wider gap.
- Ignition system strength: Modern cars with more powerful COP and distributorless ignition systems can work with a bigger gap, allowing the spark to jump farther. However, older vehicles with weaker single-coil and distributor ignition systems require smaller gaps to ensure the ignition spark jumps reliably.
NOTE: These settings can vary across different engines and ignition system designs, so refer to your owner’s manual for the recommended gap setting.
Suspect your spark plugs don’t have the proper gap?
Then, let’s walk through how to set it correctly.
How to Gap Spark Plugs Step-By-Step
Gapping a plug means carefully adjusting the space between its electrodes using a feeler gauge or another spark plug gap tool. If you’re working with platinum or iridium spark plugs, take extra care because their tips are fragile and can break easily.
Also, before you begin, ensure you’re using the right spark plug for your engine. Otherwise, even after gapping, your car may continue to perform poorly. You can quickly verify the compatibility by checking the spark plug part number, usually printed on the plug itself.
If keeping up with these steps feels overwhelming, it’s best to call an experienced technician to handle this task.
Here’s how they’ll go about spark plug gapping:
Step 1: Clean the Spark Plug
The mechanic will gently clean the debris with a wire brush. New plugs usually don’t need cleaning, but older ones often have dirt buildup around the contact points.
NOTE: The mechanic won’t use abrasive materials to clean the plugs, as this can damage the electrodes and require a complete spark plug replacement.
Step 2: Measure and Adjust the Spark Plug Gap
They’ll slide the spark plug gap tool between the center and ground electrode to measure the current gap.
If the gap is too small, they’ll use the gapping tool to bend the ground electrode outward to decrease it. Meanwhile, if the gap is too big, they’ll gently bend the spark plug electrode inward to increase it.
They’ll take extra care not to exert any force on the center electrode or its ceramic insulator since they’re fragile. The mechanic will also ensure the ground strap isn’t bent more than 0.008″ in either direction to prevent weakening the electrode.
Step 3: Check the Gap Again
After adjusting, the mechanic will re-measure the gap to confirm it matches the recommended gap setting from the owner’s manual. If the measurement is correct, the gapping process is complete.
Setting the right gap may look simple, but even a tiny mistake can cause big trouble.
Let’s see what happens when you ignore an incorrect spark plug gap.
What Happens If the Spark Gap Is Too Narrow or Too Wide?
If your vehicle’s spark plug gap is:
- Too narrow: You may get a weak spark, causing incomplete combustion, poor acceleration, and reduced power.
- Too wide: The spark may misfire entirely, leading to issues like hard starting and rough idling. This ignition problem can worsen under heavy load or high pressure when more voltage (power) is needed to jump the spark plug gap.
But what about pre-gapped spark plugs?
Do you need to check them as well?
Should You Inspect Pre-Gapped Plugs?
Yes, most modern cars have pre-gapped plugs with preset measurements, but it doesn’t mean they don’t need a checkup.
Sometimes, the gap may change while shipping or transporting the new plug. The gap may also change unintentionally during ignition system repairs. Even a small change can lead to issues, like spark plug fouling or misfires.
To avoid such problems, ask your mechanic to check the gap and adjust it per the recommended setting.
That said, it’s also essential to inspect and adjust the spark plug gap at regular intervals.
How Often Should You Check and Readjust the Spark Plugs?
You should readjust your vehicle’s spark plug gap every 30,000 to 100,000 miles or any time you replace the spark plugs.
This regular inspection is essential because:
- The gap in pre-gapped plugs can shift after installation
- Engine vibration and misfire can damage the plugs, slowly widening or reducing the gap
Got more questions about spark plug gaps?
Let’s check out some of the most common ones.
3 FAQs About Spark Plug Gap
Here are some popular queries about the spark plug gaps that you’ll find interesting:
1. Is It Better to Have a Smaller or Bigger Gap?
It depends on your engine’s design and the conditions under which the spark needs to fire:
- Smaller gap (around 0.025″ to 0.035″): This gap helps create a short and intense spark that’s more stable under high-pressure conditions, ideal for high-performance or race car engines.
- Larger gap (around 0.024″ to 0.071″): A wide gap generates a longer spark, which helps with efficient combustion in standard engines.
2. What Are the Different Types of Spark Plug Gap Tools One Can Use?
Some popular spark plug gap tools you might come across are:
- Feeler gap gauge: This gapping tool resembles a pocket knife with numerous metal blades of varying thickness. You can easily measure and adjust the spark plug gap using blades of different thicknesses. It’s ideal for platinum or iridium plugs.
- Coin-style spark plug gauge: Shaped like a coin, this gapping tool has a thin outer edge that thickens as you move around the gauge. It’s useful for copper spark plugs.
- Wire loop spark plug gauge: It’s similar to the coin-style gap gauge in shape but has a fixed set of wire loops of various thicknesses from its edges. It’s ideal for measuring iridium plugs, though its fixed loop sizes can be a drawback.
3. What Are Some Common Errors When Checking Spark Plug Gaps?
A few mistakes that can prevent proper spark plug gapping include:
- Aggressive parts handling: A spark plug electrode is made of nickel or precious metals like platinum or iridium, which can bend or break under excess force.
- Not using the correct gap tool: The wrong tool can easily alter the setting since manufacturers recommend precise gap sizes. For example, using a coin-style gap gauge for copper plugs on fragile iridium spark plugs can damage the electrodes, requiring replacement.
- Skipping the inspection of the new plug: It’s easy to assume that you can install new pre-gapped spark plugs as-is, but they often need to be adjusted for your engine. An improper gap can cause spark plug fouling and starting troubles.
Close the Gap on Engine Trouble with AutoNation Mobile Service
Using the right spark plug with the correct gap guarantees smooth ignition and steady engine performance. But if the gap changes, a simple adjustment can restore proper combustion.
Does checking and adjusting the gap seem too tedious?
No worries! AutoNation Mobile Service mechanics can help. Our technicians have the tools and experience required to adjust the gap right from your driveway.
We’re also available seven days a week and offer online bookings, so you can reserve your slot at your convenience.
Contact us, and our technicians will quickly drop by for spark plug gapping.