🔧 Legacy - Spark Plug Replacement

On your Legacy, spark plugs fire the air/fuel mix. Worn plugs can cause rough idle, misfires, and poor fuel economy. This job is tight for space on the 2.5L, but it’s very doable with the right extensions.

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.
• ⚠️ Disconnect the negative battery cable before removing the battery/airbox parts.
• ⚠️ Do not over-tighten spark plugs; stripped aluminum threads are expensive to repair.
• ⚠️ Keep dirt out of the spark plug holes; contamination can damage the engine.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Mechanic gloves
• 10mm socket
• 10mm wrench
• 3/8" drive ratchet
• 3/8" drive torque wrench (10-60 ft-lbs range)
• 3/8" drive extension 3"
• 3/8" drive extension 6"
• 3/8" drive extension 12"
• 3/8" drive wobble extension 6"
• 3/8" drive universal joint adapter
• 14mm thin-wall spark plug socket (magnetic or rubber insert)
• Flat trim tool
• Phillips screwdriver
• Shop vacuum with small nozzle
• Compressed air blow gun
• Flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (OEM-equivalent, correct heat range) - 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).
• Open the hood and disconnect the battery negative cable using a 10mm wrench.
• Set your new spark plugs aside and keep them clean; do not adjust the gap on iridium plugs.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Create working room (intake side)

• Remove the plastic intake duct/clips using a flat trim tool and Phillips screwdriver (as equipped).
• Loosen the intake hose clamp(s) using a Phillips screwdriver.
• Unbolt and lift out the air intake/airbox pieces as needed using a 10mm socket and 3/8" drive ratchet.
• Take a quick photo before disconnecting hoses.

Step 2: Create working room (battery side)

• Remove the battery hold-down using a 10mm socket and 3/8" drive ratchet.
• Disconnect the battery terminals using a 10mm wrench and remove the battery.
• If needed for access, remove the battery tray using a 10mm socket.

Step 3: Clean around each coil before removal

• For each cylinder, use compressed air blow gun and/or a shop vacuum with small nozzle to remove dirt around the ignition coil area.
• This prevents debris from falling into the spark plug tube when the plug is removed.

Step 4: Remove the ignition coil (one cylinder at a time)

• Unplug the ignition coil electrical connector by releasing the tab with a flat trim tool.
• Remove the coil retaining bolt using a 10mm socket and 3/8" drive ratchet.
• Twist the coil gently and pull it straight out.
• Torque note for reassembly: coil bolt is low torque; Torque to 7.5 Nm (5.5 ft-lbs).

Step 5: Remove the old spark plug

• Install the 14mm thin-wall spark plug socket on a 3/8" drive extension 6" (swap to 3", 12", wobble extension 6", or universal joint adapter as needed for clearance).
• A “wobble extension” is an extension that slightly angles to help in tight spaces.
• Break the plug loose with a 3/8" drive ratchet, then spin it out.
• Carefully lift the plug out with the socket.

Step 6: Install the new spark plug (prevent cross-threading)

• Place the new plug into the 14mm thin-wall spark plug socket.
• Thread it in by hand first using only the extension 6" (no ratchet at first). It should spin in smoothly.
• If it feels tight immediately, back it out and try again (cross-thread risk).
• Once seated, tighten using a 3/8" drive torque wrench: Torque to 23 Nm (17 ft-lbs).
• Do not use anti-seize on plated plugs.

Step 7: Reinstall the ignition coil

• Apply a tiny amount of dielectric grease inside the coil boot (a thin film only).
• Push the coil straight onto the spark plug until fully seated.
• Install the coil bolt using a 10mm socket, then tighten with a 3/8" drive torque wrench: Torque to 7.5 Nm (5.5 ft-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 8: Repeat for all 4 cylinders

• Do the remaining cylinders one at a time so parts don’t get mixed up.
• Use the flashlight to confirm each connector is fully latched.

Step 9: Reassemble intake and battery

• Reinstall the airbox/intake parts using a 10mm socket and Phillips screwdriver.
• Reinstall the battery tray (if removed) using a 10mm socket.
• Reinstall the battery and hold-down using a 10mm socket.
• Reconnect battery terminals using a 10mm wrench (negative cable last).

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✅ After Repair

• Start the engine and let it idle for 1-2 minutes; it should run smooth.
• If the check engine light comes on or it runs rough, shut it off and re-check coil connectors and coil seating.
• Take a short 10-minute test drive and recheck for any warning lights.

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💰 DIY vs Shop Cost

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

DIY Cost: $50-$140 (parts only)

You Save: $160-$500 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?

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