🔧 QX80 - Spark Plug Replacement

Replacing spark plugs restores smooth idle, power, and fuel economy, and helps prevent misfires that can damage the catalytic converters. On your QX80’s 5.6L V8, some plugs are easy up front, and the rear plugs typically require removing the upper intake plenum to reach the ignition coils.

Difficulty Level: Advanced | Estimated Time: 3-6 hours

Assumption: Rear-cylinder access requires upper intake plenum removal.

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⚠️ Safety & Precautions

• ⚠️ Work on a cold engine; hot aluminum threads strip easily.
• ⚠️ Disconnect the negative battery cable to prevent accidental shorting and to protect electronics.
• ⚠️ Keep dirt out of the engine; blow debris away before removing coils/plugs.
• ⚠️ Do not pull on wiring; release electrical connectors by their tabs.
• ⚠️ Avoid dropping anything into intake runners; cover openings with clean shop towels.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 8mm socket
• 12mm socket
• 3/8" drive ratchet
• 3/8" drive torque wrench (10-80 ft-lbs range)
• 1/4" drive torque wrench (in-lb range)
• 3/8" drive 5/8" spark plug socket
• 3/8" drive extension set (3", 6", 10")
• 3/8" drive universal joint
• Flathead screwdriver
• Trim clip removal tool
• Needle-nose pliers
• Hose clamp pliers
• Compressed air blow gun
• Shop towels
• Flashlight
• Magnetic pickup tool
• Feeler gauge set

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - Qty: 8
• Upper intake plenum gasket set - Qty: 1
• Throttle body gasket - Qty: 1
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and open the hood.
• Let the engine cool fully (at least 1-2 hours after driving).
• Use a 10mm socket to disconnect the negative battery terminal and isolate it so it cannot spring back.
• Label vacuum hoses/electrical connectors with tape as you remove them.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover and intake ducting

• Pull up on the engine cover to release it, or remove fasteners using a 10mm socket if equipped.
• Loosen intake tube clamps using an 8mm socket or flathead screwdriver.
• Disconnect any small breather hoses using hose clamp pliers and set the intake duct aside.

Step 2: Remove the front-bank ignition coils (easier cylinders)

• Unplug each coil connector by pressing the lock tab and pulling straight back (the connector lock is the small clip that prevents unplugging).
• Remove the coil hold-down bolt using a 10mm socket.
• Twist the coil slightly and pull it straight up to remove it.
• Before removing any plug, use compressed air blow gun to blow debris out of the spark plug well (the “well” is the deep tube the plug sits in).

Step 3: Remove and replace the front-bank spark plugs

• Remove each plug using a 5/8" spark plug socket, extension, and 3/8" ratchet.
• Check the new plug gap using a feeler gauge set. Do not bend iridium tips.
• Thread the new plug in by hand using the spark plug socket and an extension (no ratchet yet) to avoid cross-threading.
• Tighten with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).
• Apply a very small amount of dielectric grease inside the coil boot and reinstall the coil.
• Reinstall the coil bolt using a 10mm socket: Torque to 8.5 Nm (75 in-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 4: Remove the throttle body (for plenum access)

• Disconnect the throttle body electrical connector by releasing the tab and pulling straight off.
• Remove the throttle body bolts using a 10mm socket.
• Remove the throttle body and set it aside on a clean towel (do not strain the wiring).
• Replace the gasket with a new throttle body gasket.
• Reinstall bolts using a 1/4" drive torque wrench: Torque to 9 Nm (80 in-lbs).

Step 5: Remove the upper intake plenum (rear-cylinder access)

• Disconnect vacuum hoses and any electrical connectors from the plenum using needle-nose pliers and your hands; use shop towels to catch any drips.
• Remove plenum fasteners using a 12mm socket, plus extensions and a universal joint where needed.
• Lift the plenum straight up and off.
• Immediately cover exposed intake ports with shop towels. Nothing can fall in.
• Remove old gaskets and install the new upper intake plenum gasket set.

Step 6: Replace the rear-bank spark plugs

• Unplug rear-bank ignition coils and remove each coil bolt with a 10mm socket.
• Blow out each plug well using the compressed air blow gun.
• Remove plugs using the 5/8" spark plug socket, extensions, and universal joint.
• Hand-thread new plugs, then tighten with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).
• Reinstall coils and coil bolts: Torque to 8.5 Nm (75 in-lbs).
• Reconnect all coil connectors.

Step 7: Reinstall the upper intake plenum and intake ducting

• Remove the shop towels from the intake ports.
• Set the plenum into place, making sure gaskets stayed seated.
• Install plenum fasteners finger-tight first, then torque in a crisscross pattern using a 12mm socket and 3/8" torque wrench: Torque to 25 Nm (18 ft-lbs).
• Reconnect all vacuum hoses and electrical connectors.
• Reinstall the intake ducting and tighten clamps using an 8mm socket or flathead screwdriver.
• Reinstall the engine cover.

Step 8: Reconnect the battery and do a final check

• Reconnect the negative battery cable using a 10mm socket.
• Use a flashlight to verify no tools/rags are left in the engine bay.
• Make sure every coil connector and hose is reattached.

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✅ After Repair

• Start the engine and let it idle for 2-3 minutes; it should run smooth with no flashing check engine light.
• Listen for a hissing sound (vacuum leak) around the plenum and intake tube.
• If the check engine light comes on, recheck coil connectors and any plenum hoses you removed.
• Test drive 10-15 minutes, then recheck for fuel/vacuum smells or abnormal noises.

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💰 DIY vs Shop Cost

Shop Cost: $450-$950 (parts + labor)

DIY Cost: $120-$280 (parts only)

You Save: $330-$670 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 3-6 hours.

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🎯 Ready to get started?

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