🔧 Spark Plugs - Replacement

On your Sierra, the spark plugs are buried under the ignition coils on top of the engine. You’ll remove the coil packs, swap the plugs one cylinder at a time, then reinstall everything and check for a smooth idle and no misfires.

Difficulty Level: Intermediate | Estimated Time: 2-4 hours

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⚠️ Safety & Precautions

• Let the engine cool completely before starting. Hot aluminum threads can be damaged easily.
• Disconnect the negative battery cable before unplugging coils.
• Keep dirt out of the spark plug holes. A dropped bolt or grit can cause engine damage.
• Use a spark plug socket with a rubber insert. A regular socket can crack the plug.
• Do not over-tighten the new plugs. The cylinder heads are aluminum.

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🔧 Required Tools

You'll need the following tools for this repair:

• 8mm socket
• 10mm socket
• 13mm socket
• Ratchet
• 3-inch extension
• 6-inch extension
• Spark plug socket 5/8-inch
• Torque wrench
• Flat trim tool
• Dielectric grease
• Anti-seize compound
• Gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs, iridium type - Qty: 8

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Let the engine cool fully.
• Disconnect the negative battery cable before removing coil connectors.
• Work on one cylinder at a time so the plug wires and coils stay organized.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect power and open access

• Use a 10mm socket to disconnect the negative battery cable.
• Remove the engine cover by lifting it straight up if equipped.
• Keep fasteners in a tray.

Step 2: Remove the ignition coil from cylinder 1

• Use an 8mm socket to remove the ignition coil hold-down bolt.
• Twist the coil gently and pull it straight up.
• Unplug the electrical connector if needed, using a flat trim tool to release the lock carefully.

Step 3: Remove the old spark plug

• Use a 5/8-inch spark plug socket with a ratchet and extension to loosen the plug.
• Turn it out by hand once it is loose.
• Inspect the old plug for oil, heavy carbon, or damaged threads.

Step 4: Prepare and install the new spark plug

• Check the new plug gap if needed. Many iridium plugs come pre-gapped, but verify before installing.
• Apply a very small amount of anti-seize compound only if the plug manufacturer allows it.
• Thread the new plug in by hand first to avoid cross-threading.
• Use a torque wrench and 5/8-inch spark plug socket to tighten the plug to 25 Nm (18 ft-lbs).

Step 5: Reinstall the ignition coil

• Apply a small dab of dielectric grease inside the coil boot.
• Push the coil straight onto the new plug until fully seated.
• Install the coil bolt with an 8mm socket and tighten to 10 Nm (89 in-lbs).
• Reconnect the coil electrical connector.

Step 6: Repeat for the remaining cylinders

• Repeat Steps 2 through 5 for all 8 spark plugs.
• Do one plug at a time to avoid mixing parts.
• Work front to back for easier tracking.

Step 7: Reassemble and reconnect power

• Reinstall the engine cover if equipped.
• Reconnect the negative battery cable with a 10mm socket.
• Make sure all tools are removed from the engine bay.

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✅ After Repair

• Start the engine and let it idle.
• Listen for smooth running and check for a flashing check engine light.
• If the engine runs rough, recheck all coil connectors and plug seating.
• Clear any stored misfire codes with a scan tool if needed.
• Take a short test drive and confirm normal acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $400-$750 (parts + labor)

DIY Cost: $80-$180 (parts only)

You Save: $320-$570 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2-4 hours.

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🎯 Ready to get started?

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