🔧 Spark Plugs - Replacement

Your Sierra uses coil-on-plug ignition, so each spark plug sits under its own ignition coil. The job is straightforward, but working carefully matters because the plugs thread into aluminum heads and can be damaged if started crooked.

Difficulty Level: Beginner | Estimated Time: 1.5-2.5 hours

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⚠️ Safety & Precautions

• Let the engine cool completely before starting. Hot exhaust parts and cylinder heads can burn you.
• Disconnect the negative battery cable before unplugging ignition coils. This lowers the chance of accidental cranking or a spark.
• Do not use compressed air to blow dirt into the spark plug wells unless you first remove loose debris away from the openings.
• Use care when threading new plugs into the aluminum cylinder heads. Cross-threading can damage the head.
• Do not overtighten the plugs. Tightening too much can crack the plug or strip the threads.

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🔧 Required Tools

You'll need the following tools for this repair:

• 3/8-inch drive ratchet
• 3/8-inch drive torque wrench
• 5/8-inch spark plug socket
• 3-inch extension
• 6-inch extension
• 10mm socket
• Flat-blade screwdriver
• Needle-nose pliers
• Dielectric grease
• Gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plug set - Qty: 6

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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 using a 10mm socket.
• Work on one cylinder at a time so you do not mix up coils or connectors.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect battery power

• Use a 10mm socket to loosen the negative battery terminal.
• Move the cable aside so it cannot spring back to the post.

Step 2: Remove any intake ducting blocking access

• If the intake tube blocks access to the rear cylinders, loosen the hose clamps with a flat-blade screwdriver.
• Remove the duct and set it aside.
• Keep track of clamp positions.

Step 3: Remove the ignition coil from the first cylinder

• Unplug the coil electrical connector by releasing the lock tab.
• Use a 10mm socket to remove the coil hold-down bolt.
• Pull the coil straight up and off the spark plug.

Step 4: Remove the old spark plug

• Use a 5/8-inch spark plug socket, extension, and ratchet to remove the plug.
• Turn it slowly at first so you can feel if it is threaded normally.
• If it binds, stop and back it out.

Step 5: Install the new spark plug

• Check that the new plug is correct and pre-gapped to spec.
• Thread the plug in by hand first using the spark plug socket and extension.
• Once it seats, use a torque wrench to tighten it to 25 Nm (18 ft-lbs).

Step 6: Reinstall the ignition coil

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

Step 7: Repeat for the remaining cylinders

• Repeat Steps 3 through 6 for each remaining spark plug.
• Replace all 6 plugs as a set.
• Finish one cylinder before moving to the next.

Step 8: Reinstall intake ducting and reconnect battery

• Reinstall any intake ducting and tighten the clamps with a flat-blade screwdriver.
• Reconnect the negative battery cable with a 10mm socket.

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✅ After Repair

• Start the engine and let it idle.
• Listen for a smooth idle and check for misfire or flashing check engine light.
• If the engine runs rough, recheck each coil connector and plug torque.
• Take a short test drive and confirm normal acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $40-$120 (parts only)

You Save: $210-$330 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

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🎯 Ready to get started?

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