2015 GMC Acadia Spark Plug Specs & Replacement Guide

As an ASE-certified master technician, I see a lot of 2015 GMC Acadia models roll into the bay for their 100k-mile tune-ups. The Acadia is powered by GM’s ubiquitous 3.6L LFX V6 engine. While it delivers solid power and efficiency, replacing the spark plugs requires a bit more elbow grease than your average four-cylinder. Whether you are a seasoned DIYer or just want to make sure you have the right parts before heading to the shop, here is everything you need to know about your Acadia’s spark plug specifications.

Quick Reference

Note: Motorcraft is generally not recommended or cataloged as a direct-fit aftermarket option for GM’s LFX engine; stick to ACDelco, NGK, or Denso.

Why the Right Plug Matters

Spark plugs are not universally interchangeable. Your 2015 GMC Acadia was engineered specifically for Iridium spark plugs.

Iridium is a highly durable precious metal, far superior to traditional copper or standard platinum. The fine-wire iridium center electrode requires less voltage to jump the gap, resulting in a highly stable spark, better fuel economy, and a service life approaching 100,000 miles. Additionally, utilizing the correct heat range is critical. A plug that is too hot can cause pre-ignition (pinging) and engine damage, while a plug that is too cold will foul out with carbon deposits. Sticking to the OEM ACDelco 41-109 or equivalent NGK/Denso iridium plugs ensures the heat range matches GM's exact thermal demands.

How to Gap a Spark Plug

Most premium iridium spark plugs, including the ACDelco 41-109, come pre-gapped from the factory at 0.043 inches (1.1 mm). However, they can be bumped or dropped during shipping, so verifying the gap is essential.

1. Use the right tool: Do not use a cheap coin-style gauge on iridium plugs. The fine wire center electrode is extremely brittle and can snap. Instead, use a wire-style feeler gauge.
2. Measure gently: Pass the 0.043-inch wire between the center and ground electrodes. It should slide through with a slight drag.
3. Adjust if necessary: If the gap is too tight, use the bending tool on the gauge to gently pry the ground strap away from the center electrode. Never pry against the delicate iridium tip itself!

Replacement Procedure Tips

The 2015 Acadia utilizes a Coil-on-Plug (COP) ignition system, meaning there are no spark plug wires or distributors—just individual ignition coils bolted directly over each plug.

The Intake Manifold Challenge: Because the 3.6L V6 is mounted transversely, the front three plugs (Bank 2) are staring right at you when you open the hood. The rear three (Bank 1), however, are buried under the intake manifold plenum against the firewall. While some contortionists manage to replace the rear plugs by removing the cowl and reaching blindly, the factory-approved (and generally less frustrating) method is to remove the upper intake manifold. Make sure you order a new intake manifold gasket set before starting this job.

The Anti-Seize Debate: GM advises against using anti-seize compound on their modern ACDelco spark plugs. These plugs feature a special zinc-nickel or trivalent plating on the threads designed to prevent seizing in the aluminum cylinder head. Adding anti-seize acts as a lubricant, which can easily cause you to over-torque the plug and strip the cylinder head threads.

Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the new ignition coil boots. This prevents the rubber from fusing to the ceramic ribbed shell of the spark plug, making future removal much easier and preventing high-voltage arcing.

Known Issues

While you won't face the infamous two-piece spark plug breakage issues seen in older Ford 3-valve engines, the GM 3.6L V6 has its own quirks. Because the rear bank is so difficult to access, we often see Acadias come into the shop where a previous owner or lazy mechanic only replaced the front three plugs. This leads to a severe imbalance in ignition performance, triggering misfires, poor fuel economy, and potentially damaging the catalytic converters. Always replace all six plugs at the same time. Additionally, the ignition coils on this engine can become weak due to extreme heat trapped at the rear of the engine bay. If you have a misfire code (like P0301, P0303, or P0305) on the rear bank, it is highly recommended to replace the rear ignition coils while the intake manifold is already off to save on future labor.

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