🔧 Legacy - Spark Plug Replacement

Your Legacy uses one spark plug per cylinder to ignite the air/fuel mix. Over time the plugs wear, which can cause rough idle, misfires, and worse fuel economy. Replacing them restores strong ignition and smooth running.

Difficulty Level: Intermediate | Estimated Time: 1.5-3.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and damaged threads in the aluminum cylinder heads.
• ⚠️ Disconnect the negative battery terminal if you’ll be moving wiring harnesses near the battery or using metal tools in tight spaces.
• ⚠️ Do not over-tighten spark plugs—over-torque can strip threads in the head.
• ⚠️ Keep dirt out of the plug holes; debris can fall into the cylinder.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 3/8" drive ratchet
• 3/8" drive torque wrench (5-30 ft-lbs range)
• 14mm thin-wall spark plug socket (magnetic or rubber insert)
• 3/8" drive 3" extension
• 3/8" drive 6" extension
• 3/8" drive wobble extension
• Trim clip removal tool
• Flathead screwdriver
• Needle-nose pliers
• Small torque angle not required
• Flashlight
• Compressed air blow gun

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (correct spec for your Legacy) - 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 completely (at least 1 hour after driving).
• Open the hood and remove any loose jewelry or dangling sleeves.
• Take a quick photo of hose routing first.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Lift the cover straight up by hand. If it uses clips, use a trim clip removal tool (a small pry tool for plastic fasteners).

Step 2: Create working room on the left side (driver side)

• Use a flathead screwdriver to loosen the air intake hose clamp(s).
• Use needle-nose pliers to release any spring clamps on small hoses (if present).
• Move the intake duct/air snorkel aside as needed for access. (You don’t always need to fully remove the air box.)

Step 3: Create working room on the right side (passenger side)

• If access is tight near the washer tank/neck area, remove the fasteners holding the neck or nearby brackets using a 10mm socket and 3/8" drive ratchet.
• Carefully reposition parts without kinking hoses or straining wiring.

Step 4: Unplug and remove one ignition coil at a time

• Pick one cylinder to start. Do one coil + one plug at a time to avoid mixing connectors.
• Press the electrical connector lock tab, then unplug the coil.
• Remove the coil hold-down bolt using a 10mm socket and 3/8" drive ratchet.
• Twist the coil slightly, then pull it straight out.
• If it feels stuck, twist—don’t pry hard.

Step 5: Clean the spark plug well

• Blow out the area around the plug using a compressed air blow gun so debris doesn’t fall into the cylinder.
• Use a flashlight to confirm the well is clean.

Step 6: Remove the old spark plug

• Install a 14mm thin-wall spark plug socket on a 3/8" drive extension (use a wobble extension if the angle is tight; it allows a slight bend).
• Use a 3/8" drive ratchet to loosen the plug counterclockwise, then spin it out by hand with the ratchet/extension.
• Lift the plug out with the socket.

Step 7: Install the new spark plug (start by hand)

• Place the new plug into the 14mm thin-wall spark plug socket (the insert helps hold it).
• Carefully lower it into the hole.
• Thread it in by hand only using the extension (no ratchet at first). It should spin smoothly several turns.
• If it binds, back it out and restart—this prevents cross-threading.

Step 8: Torque the spark plug

• Set your 3/8" drive torque wrench (5-30 ft-lbs range).
• Tighten the plug to Torque to 18 Nm (13 ft-lbs).

Step 9: Reinstall the ignition coil

• Apply a small dab of dielectric grease inside the coil boot (this helps prevent moisture and makes future removal easier).
• Push the coil straight onto the plug until fully seated.
• Install the coil bolt using a 10mm socket and 3/8" drive ratchet, then Torque to 6.4 Nm (57 in-lbs) with the torque wrench if it can measure inch-lbs; otherwise snug gently (do not over-tighten).
• Reconnect the electrical connector until it clicks.

Step 10: Repeat for the remaining 3 cylinders

• Repeat Steps 4–9 for each remaining plug.
• Keep coils and connectors matched per cylinder.

Step 11: Reinstall intake ducting/brackets and engine cover

• Reposition intake ducting and hoses, then tighten clamps using a flathead screwdriver.
• Reinstall any 10mm fasteners using a 10mm socket and 3/8" drive ratchet.
• Reinstall the engine cover by pressing it back into place by hand.

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✅ After Repair

• Start the engine and let it idle for 30–60 seconds. It should run smooth with no shaking.
• Listen for air leaks (hissing) around the intake hose connections you moved.
• If the check engine light comes on or it runs rough, re-check each coil connector click-in and coil seating.
• Optional: If you have a scan tool, clear any stored misfire codes and recheck for pending codes after a short drive.

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💰 DIY vs Shop Cost

Shop Cost: $300-$550 (parts + labor)

DIY Cost: $40-$100 (parts only)

You Save: $200-$450 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-3.0 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.