🔧 Spark Plugs - Replacement

On your Sierra, the spark plugs are located under the ignition coils on the 6.2L V8. This job is mostly careful disassembly, then reassembly with the correct gap and torque so you do not crack a plug or strip the heads.

Difficulty Level: Intermediate | Estimated Time: 2-3 hours

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⚠️ Safety & Precautions

• Work only on a completely cold engine. Hot aluminum cylinder heads can be damaged if plugs are removed too soon.
• Disconnect the negative battery cable before unplugging ignition coils.
• Keep dirt out of the plug wells. Debris can fall into the cylinders if you remove a plug carelessly.
• Do not use anti-seize on the plug threads unless the plug maker specifically says to. Most modern plugs are pre-coated.
• Use a torque wrench. Overtightening can damage the threads in the cylinder head.

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🔧 Required Tools

You'll need the following tools for this repair:

• 5/8-inch spark plug socket
• 3/8-inch drive ratchet
• 3-inch extension
• 6-inch extension
• 8mm socket
• Torque wrench
• Flat-blade trim tool
• Needle-nose pliers
• Feeler gauge
• Dielectric grease
• Safety glasses
• Mechanic gloves

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plug set - 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 unplugging ignition coils.
• Have the new plugs ready and check the gap before installation. Pre-gapped does not always mean correct.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect power and open access

• Use an 8mm socket to disconnect the negative battery cable.
• Remove the engine cover by lifting it straight up.
• If needed for room, loosen the intake duct with a flat-blade trim tool and set it aside.

Step 2: Remove one ignition coil at a time

• Use an 8mm socket and 3/8-inch drive ratchet to remove the coil bolt.
• Unplug the coil connector by pressing the tab and pulling straight back.
• Twist the coil boot slightly and pull the coil straight up.
• Do one cylinder at a time.

Step 3: Remove the spark plug

• Use a 5/8-inch spark plug socket with a 3-inch extension and ratchet to loosen the plug.
• Once loose, remove it by hand with the socket to avoid cross-threading.
• Inspect the old plug for heavy oil, fuel, or white blistering. That can point to other engine issues.

Step 4: Prepare and install the new plug

• Check the new plug gap with a feeler gauge. Set it to 0.040 in if needed.
• Start the plug into the head by hand using the 5/8-inch spark plug socket and extension.
• Thread it in several turns by hand first. This prevents cross-threading.
• Use a torque wrench to tighten the plug to 18 Nm (13 ft-lbs).

Step 5: Reinstall the coil

• Apply a small amount of dielectric grease inside the coil boot. This helps prevent moisture and makes future removal easier.
• Push the coil straight onto the plug until it seats fully.
• Reinstall the coil bolt with an 8mm socket and tighten to 10 Nm (89 in-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 6: Repeat for all 8 cylinders

• Repeat Steps 2 through 5 for each remaining cylinder.
• Keep the old plugs in order if you want to compare wear patterns.

Step 7: Reassemble and reconnect power

• Reinstall the intake duct and engine cover.
• Reconnect the negative battery cable with an 8mm socket.

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✅ After Repair

• Start the engine and let it idle.
• Listen for a smooth idle and check for a flashing or steady check-engine light.
• If the engine runs rough, recheck every coil connector and make sure each boot is seated fully.
• Drive gently at first and verify normal acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $280-$550 (parts + labor)

DIY Cost: $70-$180 (parts only)

You Save: $210-$370 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?

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