🔧 Lancer - Spark Plug Replacement

On your Lancer, the spark plugs sit under the ignition coils on top of the engine. Replacing them restores strong ignition, helps prevent misfires, and keeps fuel economy and idle smooth.

Difficulty Level: Beginner | Estimated Time: 0.8-1.5 hours

Assumption: 2.4L uses coil-on-plug ignition under the top engine cover.

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⚠️ Safety & Precautions

• 🧯 Work on a fully cool engine to avoid burns and stripped threads.
• 🔋 Turn ignition OFF and keep the key away so the coils can’t energize.
• 🧤 Blow dirt away from the plug wells before removing plugs to prevent debris falling into the cylinders.
• ⚠️ Do not over-tighten spark plugs—aluminum cylinder head threads can strip.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 1/4" drive ratchet
• 3/8" drive ratchet
• 10mm socket
• 5/8" spark plug socket
• 3/8" drive extension set (3", 6", 10")
• Torque wrench (3/8" drive, 10-60 Nm range)
• Trim clip tool
• Compressed air blow gun
• Feeler gauge set
• Small flathead screwdriver

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (iridium/platinum, correct for 2.4L) - 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 (warm aluminum threads strip easily).
• If your hands will be near exposed electrical connectors, disconnect the negative battery cable using a 10mm socket.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the top engine cover (if equipped)

• Use a trim clip tool to release any plastic clips, then lift the cover off by hand.
• If bolts are present, remove them with a 10mm socket.

Step 2: Unplug and remove the ignition coils

• Locate the four ignition coils on top of the engine (one per cylinder).
• Release each electrical connector:
  • If the lock tab is tight, gently help it with a small flathead screwdriver (do not pry hard).
• Remove the coil hold-down bolt using a 10mm socket.
• Twist the coil boot slightly, then pull the coil straight up and out.
• Torque spec for reassembly: Torque coil bolts to 10 Nm (89 in-lbs).

Step 3: Clean the spark plug wells

• Blow out each plug well using a compressed air blow gun while wearing safety glasses.
• Tip: Dirt in the cylinder can score walls.

Step 4: Remove the old spark plugs

• Install a 5/8" spark plug socket on a 3/8" drive extension and 3/8" drive ratchet.
• Lower the socket straight down onto the spark plug and loosen it.
• Once loose, spin it out carefully and lift it out with the spark plug socket.

Step 5: Check the new spark plug gap (only if your plug maker allows it)

• Use a feeler gauge set to verify the gap matches the plug specification supplied with your plugs.
• If the plugs are iridium with a very fine center tip, do not force-bend the electrode.
• Tip: Many iridium plugs are “pre-gapped.”

Step 6: Install the new spark plugs by hand first

• Place a new plug into the 5/8" spark plug socket (rubber insert holds it).
• Thread it into the head by hand using only the extension (no ratchet at first).
• If you feel resistance early, stop and restart—this prevents cross-threading.

Step 7: Torque the spark plugs

• Set your torque wrench (3/8" drive, 10-60 Nm range).
• Torque spark plugs to 25 Nm (18 ft-lbs).
• Do not add anti-seize unless the plug manufacturer specifically requires it (it can cause over-tightening).

Step 8: Reinstall ignition coils

• Apply a tiny smear of dielectric grease inside each coil boot (this helps prevent moisture sticking). Dielectric grease is a non-conductive silicone grease used to protect rubber boots.
• Push each coil straight down until it fully seats on the plug.
• Install the coil bolts with a 10mm socket, then Torque coil bolts to 10 Nm (89 in-lbs) using the torque wrench.
• Reconnect each electrical connector until it clicks.

Step 9: Reinstall the engine cover and reconnect the battery (if disconnected)

• Reinstall the cover and fasteners using a 10mm socket or by pressing clips in by hand.
• If you disconnected it earlier, reconnect the negative battery cable using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 30-60 seconds. It should run smooth with no shaking.
• If the check engine light is on or the engine misfires, re-check coil connectors and coil seating.
• Take a short test drive, then recheck for any new warning lights.

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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 0.8-1.2 hours.

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🎯 Ready to get started?

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