🔧 Legacy - Spark Plug Replacement

On your Legacy, the spark plugs wear over time and can cause rough idle, misfires, and worse fuel economy. Replacing them restores strong ignition, but access is tight, so you’ll work slowly and use extensions to reach each plug.

Difficulty Level: Intermediate | Estimated Time: 2-3 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a cold engine to avoid burns and damaged threads.
• ⚠️ Disconnect the negative battery terminal to prevent accidental short circuits.
• ⚠️ Do not pull on wiring; unplug coils by the connector body.
• ⚠️ Keep dirt out of the spark plug holes—debris can damage the engine.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 10mm wrench
• Ratchet (3/8" drive)
• 3/8" torque wrench (10-50 ft-lb range)
• 14mm spark plug socket (thin-wall, 3/8" drive)
• 3/8" extension set (3", 6", 10")
• 3/8" wobble extension (specialty)
• 3/8" universal joint adapter
• Trim clip tool
• Flathead screwdriver
• Needle-nose pliers
• Compressed air blow gun
• Flashlight
• Feeler gauge set
• OBD2 scan tool (optional)

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (OEM-equivalent) - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool fully (at least 1-2 hours).
• Open the hood and use a 10mm wrench to disconnect the negative battery terminal.
• Take a quick photo before unplugging anything.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the intake ducting (for access)

• Use a flathead screwdriver to loosen the hose clamps on the intake duct.
• Use a trim clip tool to pop any plastic clips holding the duct/resonator pieces.
• Lift the ducting out and set it aside.

Step 2: Create room on each side of the engine bay

• On the battery side, use a 10mm socket and ratchet (3/8" drive) to remove the battery hold-down, then lift the battery out carefully.
• On the washer filler neck (if it blocks access), use needle-nose pliers for any clips and gently move it aside without kinking the hose.
• More space = less frustration.

Step 3: Unplug and remove the ignition coils

• Each spark plug has an ignition coil on top (the pencil-shaped part).
• Press the tab and unplug the coil connector by hand (use a flashlight to see the tab clearly).
• Use a 10mm socket and ratchet (3/8" drive) to remove the coil retaining bolt.
• Twist the coil gently, then pull it straight out.
• Don’t pry on the plastic connector.

Step 4: Clean around each spark plug hole

• Use compressed air blow gun to blow dirt/debris away from the spark plug tube before removing the plug.
• This prevents grit from falling into the cylinder.

Step 5: Remove the old spark plugs

• Install the 14mm spark plug socket (thin-wall, 3/8" drive) onto a 3/8" extension set (3", 6", 10").
• If the angle is tight, add a 3/8" wobble extension (specialty) or 3/8" universal joint adapter to align with the plug.
• Use the ratchet (3/8" drive) to break the plug loose, then spin it out.
• Lift the plug out with the socket.

Step 6: Check the new plug gap (do not force it)

• Use a feeler gauge set to confirm the gap matches the plug’s spec on the box.
• Most iridium plugs come pre-gapped—do not bend the tiny center electrode.
• If it’s off, exchange the plug.

Step 7: Install the new spark plugs

• Place the new plug into the 14mm spark plug socket (thin-wall, 3/8" drive).
• Carefully lower it into the hole using your 3/8" extension set (3", 6", 10").
• Thread it in by hand first using only the extension (no ratchet) to avoid cross-threading.
• Once finger-tight, use a 3/8" torque wrench (10-50 ft-lb range) to tighten: Torque to 21 Nm (15 ft-lb).

Step 8: Reinstall ignition coils

• Add a small smear of dielectric grease inside the coil boot (helps moisture sealing).
• Push the coil straight onto the plug until it fully seats.
• Install the coil bolt using a 10mm socket and ratchet (3/8" drive), then tighten with the 3/8" torque wrench: Torque to 7.5 Nm (66 in-lb).
• Reconnect the electrical connector until it clicks.

Step 9: Reassemble what you removed

• Reinstall the battery and hold-down using a 10mm socket and ratchet (3/8" drive).
• Reconnect the negative battery terminal using a 10mm wrench.
• Reinstall intake ducting and tighten clamps with a flathead screwdriver.

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✅ After Repair

• Start the engine and let it idle for 1-2 minutes. It should run smooth with no shaking.
• Listen for any hissing (intake leak) around the ducting.
• If the check engine light is on, use an OBD2 scan tool (optional) to read codes and confirm no misfires are present.
• Take a short test drive, then recheck that intake clamps and battery terminals are tight.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $40-$120 (parts only)

You Save: $130-$410 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.