Your spark plugs play a vital role in your engine’s performance and efficiency. One often-overlooked detail that can make a big difference is the spark plug gap — the distance between the center and ground electrodes. If this gap isn’t set correctly, your engine may misfire, idle roughly, or suffer reduced fuel economy.
In this guide, we’ll walk you through how to check and adjust the spark plug gap to keep your engine running smoothly.
Why Spark Plug Gap Matters
The spark plug gap controls the size of the spark that ignites the air-fuel mixture in your engine’s cylinders.
A gap that’s too small may cause a weak spark, leading to incomplete combustion and poor performance.
A gap that’s too wide can make it difficult for the spark to jump across, especially under high compression, leading to misfires.
Maintaining the correct gap ensures efficient combustion, smoother acceleration, and optimal fuel efficiency.
What You’ll Need
Before you begin, gather these tools:
- A spark plug gap gauge or feeler gauge
- A spark plug gapping tool (or small adjustment tool)
- A clean cloth
- Your vehicle’s service manual (for the correct gap specification)
Step 1: Locate the Recommended Gap
Check your owner’s manual or the under-hood emissions label for the manufacturer’s recommended spark plug gap. Different engines require different gap sizes, typically between 0.6 mm and 1.3 mm (0.024–0.052 inches).
Step 2: Measure the Gap
Hold the spark plug with the electrodes facing you.
Insert the correct-size wire from your gap gauge between the center and ground electrodes.
You should feel a slight drag — that indicates the correct gap.
If the gauge passes through too easily or won’t fit, the gap needs adjustment.
Step 3: Adjust the Gap
To widen the gap: Gently bend the ground electrode outward using the gapping tool.
To narrow the gap: Carefully tap the ground electrode inward.
Re-check the gap with your gauge until it matches the specification.
⚠️ Tip: Never pry or bend the center electrode — it can easily break or damage the insulator.
Step 4: Reinstall or Replace
Once all spark plugs are properly gapped, reinstall them according to your vehicle’s torque specifications. If the electrodes show wear, heavy deposits, or damage, it’s best to replace the plug entirely.
Final Thoughts
A properly gapped spark plug ensures consistent ignition, better combustion, and improved engine efficiency. Spending a few extra minutes checking and adjusting the gap can go a long way toward preventing engine issues and maximizing performance.