🔧 Explorer - Spark Plug Replacement

On your Explorer, the spark plugs ignite the air/fuel mix. Worn plugs can cause misfires, rough idle, poor fuel economy, and hard starts. This job is mostly about careful access and installing the new plugs without cross-threading.

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.
• ⚠️ Do not pull on wires—disconnect coils by the connector and coil body.
• ⚠️ Keep dirt out of the plug holes; blow debris out before removing plugs.
• ⚠️ If you disconnect the battery, you may lose radio presets.

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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
• 7mm socket
• 8mm socket
• 5/8" spark plug socket
• 3/8" drive extension set (3", 6", 10")
• 3/8" drive universal joint
• Torque wrench (3/8" drive, inch-lb/ft-lb capable)
• Flat-blade screwdriver
• Compressed air blow gun
• Feeler gauge set (spark plug gap tool)
• Small pick tool

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (correct fit for your Explorer 4.0L) - Qty: 6
• Dielectric grease - Qty: 1
• Ignition coil boots (optional, if cracked/swollen) - Qty: 6

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Open the hood and let the engine cool completely (at least 1 hour).
• If you choose to disconnect the battery: use an 8mm socket to remove the negative terminal and tuck it aside.
• Know what “coil-on-plug (COP)” means: the ignition coil sits directly on top of each spark plug.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Use an appropriate 8mm socket or a flat-blade screwdriver (depending on fastener style) to remove the cover fasteners.
• Lift the cover off and set it aside.

Step 2: Clear access around the coils

• If the intake tube/duct blocks access, loosen clamps using a flat-blade screwdriver and reposition it as needed.
• Work one cylinder at a time so nothing gets mixed up.
• One coil at a time prevents connector mix-ups.

Step 3: Unplug one ignition coil

• Press the electrical connector lock tab (use a small pick tool gently if needed) and pull the connector straight off.
• Do not pry hard on the connector—plastic gets brittle with age.

Step 4: Remove the coil and bolt

• Remove the coil hold-down bolt using a 7mm socket and 1/4" drive ratchet.
• Twist the coil slightly to break it loose, then pull it straight up and out.
• Set the coil where it won’t get dirty.

Step 5: Clean the spark plug well

• Blow compressed air into the spark plug hole using a compressed air blow gun.
• This prevents grit from falling into the cylinder when the plug comes out.

Step 6: Remove the old spark plug

• Install a 5/8" spark plug socket with the needed 3/8" drive extensions and a 3/8" drive universal joint if angled access is tight.
• Use a 3/8" drive ratchet to loosen and remove the spark plug.
• If it feels stuck, stop and work it back-and-forth gently to avoid damaging threads.

Step 7: Check and set the new plug gap

• Use a feeler gauge set to check the gap.
• Set the gap to 0.054 in (1.37 mm) unless your new plug’s box label specifies otherwise for your exact application.
• Do not pry against the center electrode; adjust carefully.

Step 8: Install the new spark plug (by hand first)

• Place the new plug into the 5/8" spark plug socket.
• Thread it in by hand using only the extension (no ratchet) until fully seated. This helps prevent cross-threading.
• Then use a torque wrench to tighten: Torque to 15 Nm (11 ft-lbs).
• Hand-thread first—cross-threading is expensive.

Step 9: Reinstall the coil

• Put a small dab of dielectric grease inside the coil boot (it helps prevent moisture and makes future removal easier).
• Push the coil straight down onto the plug until fully seated.
• Install the hold-down bolt using a 7mm socket, then tighten with a torque wrench: Torque to 7 Nm (62 in-lbs).

Step 10: Reconnect the coil connector

• Push the connector on until it clicks/locks.
• Repeat Steps 3–10 for the remaining 5 cylinders.

Step 11: Reinstall the intake tube and engine cover

• Reposition any intake ducting and tighten clamps using a flat-blade screwdriver.
• Reinstall the engine cover fasteners using an 8mm socket (or the original fastener tool type).

Step 12: Reconnect the battery (if disconnected)

• Reconnect the negative battery terminal using an 8mm socket.

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✅ After Repair

• Start the engine and let it idle for 1–2 minutes. It should run smooth.
• If you have a check engine light or rough running, shut it off and re-check that every coil connector is fully clicked in.
• 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: $45-$120 (parts only)

You Save: $205-$330 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.