How to Change and Gap a Spark Plug

Spark plugs provide the jolt of electricity required to ignite the combustion process. But they don’t last forever. Conventional copper spark plugs must generally be replaced every 5,000 to 10,000 miles or every few years. Iridium spark plugs, meanwhile, may last up to around 30,000 miles. Regardless, all spark plugs must eventually be changed out, and when that happens, they must also be gapped.

Changing and gapping your spark plugs might seem like a daunting task, especially if you’re a beginner. But with the right tools, some patience, and the right know-how, it’s something you can easily do yourself.

With that said, let’s discuss how to change and gap your spark plugs as someone new to car maintenance.

Why Must Spark Plugs Be Changed Regularly?

Spark plugs are subjected to a lot of wear and tear under normal operation. The electrodes of a spark plug, which are responsible for creating the electrical current required to ignite the combustion process, may erode over time.

The gap between electrodes may also widen or narrow over time, leading to the engine misfiring under full throttle, and possibly setting misfire fault codes.. Other common signs of worn spark plugs include a car that seems to run “rough” or doesn’t start easily.

In short, spark plugs are wearable items that are essential to normal and efficient engine operation, meaning that replacing them according to mechanic or OE recommendations is extremely important.

How to Change Spark Plugs

1. Prepare the Engine: Allow the engine to cool down attempting to replace spark plugs. Then, gather the tools you will need, including a spark plug socket, ratchet, and extension. Next, remove the negative battery connector.
2. Find the Spark Plugs: You might need to remove the engine cover (if equipped) to find the spark plugs. Usually, your owner’s manual will have information on where they are in your vehicle.
3. Remove the Old Spark Plugs: Use a spark plug socket to unscrew and remove each plug. Make sure you remove one plug at a time.
4. Inspect the New Spark Plugs: Set the gap on each new spark plug (more on that later) and ensure it conforms to manufacturer recommendations.
5. Install the New Spark Plugs: Thread the new spark plug into the engine by hand to prevent cross-threading, then use a torque wrench to tighten them to the manufacturer's specifications.
6. Reassemble: After the new spark plugs are secure, reattach any engine covers or components that were previously removed, including the negative battery terminal.

Do Spark Plugs Come Pre Gapped?

Most spark plugs do come manufacturer pre gapped, yes. However, it’s common for vehicles which have been upgraded to higher performance to need tighter spark plug gaps.

What is spark plug gapping exactly? Simply put, it’s the process of checking to see if the distance, or gap, between the spark plug’s ground or side electrode and central electrode, conforms to OE or mechanic recommendations.

For stock cars, follow OE recommendations. For vehicles that have been tuned & modded, check with your tuner, or in our support documentation for your tune.

How to Gap Spark Plugs

To gap spark plugs correctly, you’ll need a spark plug gap tool. These come in several types, including feeler gauges, wire-type gap gauges, and coin style gauges.

While coin style gapping tools may seem like the easiest to use, you should avoid using them with high-end spark plugs.

Feeler gauges are best for premium spark plugs, such as those made with iridium, because they slide in and out of the gap without putting too much pressure or leverage on the central electrode, which for iridium spark plugs, is very brittle and easily broken.

To gap a spark plug with a feeler gauge, you’ll need access to one. You’ll also need a pair of needle nose pliers, and a hard surface (preferably a vice). Then, here’s what to do:

1. First, understand your recommended gap distance. Usually, this is somewhere around 0.018 inches and 0.032 inches.
2. Next, measure the distance using a feeler gauge. You’ll want to choose the individual feeler that is labeled with the desired distance. If you don’t have one with the distance, stack two feelers on top of each other to achieve the desired distance. Then, test the gap. You should be able to slide the feeler(s) in and out with some resistance.
3. If the feeler gets stuck, the gap is too small and should be adjusted. If the feeler slides in and out easily with a noticeable gap or is very loose, it’s too wide and should also be adjusted.
4. For a gap that is too small, use the needle nose pliers to very gently pry it open little by little, measuring using the feeler gauge to ensure the proper gap. Be careful not to touch the central electrode.
5. For a gap that is too big, tap the end of the ground/side electrode against a vice or hard surface using light to moderate pressure, then check the gap. Remember, when gapping, you’re looking to make changes that are fractions of an inch, so it's better to start small and make gradual improvements.
6. Test each spark plug to ensure the gap is correct, and repeat this process if the gap doesn’t conform to recommendations.

Get the Performance Parts You Need at Integrated Engineering

Ready to upgrade your VW or Audi with premium performance parts to get it running in its best shape ever?

Shop all IE performance parts now.