🔧 MDX - Spark Plug Replacement

On your MDX, the spark plugs sit under the ignition coils. The front bank is easy to reach, but the rear bank requires removing the upper intake plenum so you can access the coils and plugs safely.

Difficulty Level: Intermediate | Estimated Time: 2.5-4.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and to protect aluminum threads.
• ⚠️ Disconnect the negative battery cable to prevent accidental shorting when unplugging coils and sensors.
• ⚠️ Keep dirt out of the intake ports; cover openings with clean shop towels immediately.
• ⚠️ Do not over-tighten spark plugs; the cylinder heads are aluminum.
• ⚠️ If you smell fuel heavily after reassembly, stop and recheck all connections before starting.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 3/8" drive ratchet
• 3/8" drive torque wrench (5–80 N·m range)
• 10mm socket
• 12mm socket
• 5/8" spark plug socket (rubber insert)
• 3/8" drive extension set (3", 6", 10")
• 3/8" drive universal joint (swivel)
• Flat-blade screwdriver
• Hose clamp pliers
• Trim clip removal tool
• Needle-nose pliers
• Compressed air blow gun
• Shop towels
• Magnetic pickup tool
• Small flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (laser iridium, OEM-spec) - Qty: 6
• Upper intake plenum gasket set - Qty: 1
• Throttle body gasket - Qty: 1
• Dielectric silicone 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 (ideally 2+ hours).
• 🧰 Disconnect the negative battery cable using a 10mm socket and isolate it so it can’t spring back.
• 🧰 Take a quick photo of hose and connector routing before you remove anything.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull up to release the cover from its rubber grommets; use a trim clip removal tool if it’s stubborn.

Step 2: Remove the air intake tube (to make room)

• Loosen the hose clamps using a flat-blade screwdriver.
• Unplug any intake tube connector(s) by pressing the lock tab with your fingers (use needle-nose pliers only if needed).
• Lift the tube out and set it aside.

Step 3: Replace the front-bank spark plugs (easiest bank)

• Unplug each ignition coil connector by pressing the release tab and pulling straight back.
• Remove each coil hold-down bolt using a 10mm socket, then pull the coil straight up and out.
• Blow debris away from each spark plug well using a compressed air blow gun.
• Remove the spark plug using a 5/8" spark plug socket (rubber insert), a 3/8" drive extension, and a 3/8" drive ratchet.
• Install the new spark plug by hand first using the spark plug socket and extension (no ratchet) to avoid cross-threading.
• Tighten the spark plug with a 3/8" drive torque wrench: Torque to 18 N·m (13 ft-lbs).
• Apply a thin film of dielectric silicone grease inside the coil boot, then reinstall the coil.
• Tighten the coil bolt using a 10mm socket: Torque to 12 N·m (9 ft-lbs).

Tip: Do one cylinder at a time.

Step 4: Remove the upper intake plenum (to reach the rear bank)

• Place shop towels around the work area to catch dropped fasteners.
• Disconnect the electrical connectors on the throttle body/nearby sensors by hand; use a small flashlight to find the lock tabs.
• Remove any vacuum/breather hoses from the plenum using hose clamp pliers and needle-nose pliers as needed.
• Remove the plenum mounting fasteners using a 12mm socket and 3/8" drive ratchet.
• Carefully lift the plenum off; if it sticks, gently work it loose by hand (do not pry hard on plastic mating surfaces).
• Immediately cover the exposed intake openings with shop towels so nothing can fall in.

Tip: Label hoses with tape.

Step 5: Replace the rear-bank spark plugs

• Remove the towels only from the cylinder you’re working on, and keep the other openings covered.
• Unplug ignition coil connectors, then remove coil bolts with a 10mm socket and pull coils out.
• Blow debris out of the plug wells using a compressed air blow gun.
• Remove spark plugs using a 5/8" spark plug socket, extension, and a universal joint (swivel) (a swivel is a hinged adapter that lets the socket bend to fit tight angles).
• Hand-thread the new plugs in using the spark plug socket and extension.
• Tighten each spark plug with a torque wrench: Torque to 18 N·m (13 ft-lbs).
• Reinstall coils and tighten coil bolts: Torque to 12 N·m (9 ft-lbs).

Step 6: Reinstall the upper intake plenum with new gaskets

• Remove old gaskets and install the new upper intake plenum gasket set (match orientation exactly).
• Set the plenum back in place carefully (do not pinch wires or hoses).
• Start all plenum fasteners by hand, then tighten evenly using a 12mm socket.
• Tighten plenum fasteners with a torque wrench: Torque to 22 N·m (16 ft-lbs).
• If you removed/loosened the throttle body, install the new throttle body gasket and tighten fasteners with a 10mm socket: Torque to 12 N·m (9 ft-lbs).
• Reconnect all vacuum/breather hoses using hose clamp pliers.
• Reconnect all electrical connectors by pushing until they click.

Step 7: Reinstall the intake tube and engine cover

• Reinstall the intake tube and tighten clamps using a flat-blade screwdriver.
• Reinstall the engine cover by pressing it onto the grommets.
• Reconnect the negative battery cable using a 10mm socket.

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✅ After Repair

• 🧪 Start the engine and listen for a smooth idle (no shaking/misfire).
• 🧪 Check for a hissing sound (vacuum leak) around the plenum and intake tube.
• 🧪 If the battery was disconnected, perform an idle relearn: warm engine fully, turn all accessories off, and let it idle undisturbed for about 5 minutes.
• 🧪 If the check engine light comes on, scan for codes and recheck coil connectors and any vacuum hoses.

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💰 DIY vs Shop Cost

Shop Cost: $450-$900 (parts + labor)

DIY Cost: $90-$220 (parts only)

You Save: $360-$680 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2.5-4.0 hours.

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🎯 Ready to get started?

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