🔧 3500 - Spark Plug Replacement

Your 3500’s 6.4L HEMI uses spark plugs to ignite the air/fuel mixture. Worn plugs can cause misfires, rough idle, poor MPG, and hard starts. This job is straightforward, but access is tight on the rear cylinders, so take your time.

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

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and damaged threads.
• ⚠️ Disconnect the negative battery cable to prevent accidental shorts while working near coils and wiring.
• ⚠️ Do not use anti-seize on modern plated spark plugs; it can cause over-tightening.
• ⚠️ Start spark plugs by hand first to prevent cross-threading the cylinder head.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 3/8" ratchet
• 3/8" torque wrench (ft-lb capable)
• 5/8" spark plug socket
• 3/8" extension set (3", 6", 10")
• 3/8" swivel adapter
• Flat trim tool
• Compressed air blow gun
• Dielectric grease

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (6.4L HEMI, OEM-style) - Qty: 16
• Coil boot set - Qty: 8 (optional)

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📋 Before You Begin

• 🅿️ Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool completely (at least 1 hour after driving).
• Use a 10mm socket to disconnect the negative battery cable and move it aside.
• Quick check: your 6.4L HEMI typically has 16 spark plugs (two per cylinder). You’ll see a coil on top and usually a second plug down the side of the cylinder head with a plug boot.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Pull up evenly on the cover using your hands or a flat trim tool if it’s stuck.

Step 2: Identify cylinder locations (helps you stay organized)

• Passenger side cylinders are typically 1-3-5-7 front to rear; driver side are 2-4-6-8 front to rear.
• Do one cylinder at a time.

Step 3: Remove the coil (top plug) for one cylinder

• Unplug the coil electrical connector by pressing the lock tab with your fingers.
• Remove the coil hold-down bolt using a 10mm socket and 3/8" ratchet.
• Twist the coil boot slightly, then pull the coil straight up.
• Definition: Dielectric grease is a silicone grease that helps prevent moisture and makes boots easier to remove later.

Step 4: Remove the top spark plug

• Blow out dirt from the plug well using a compressed air blow gun.
• Remove the plug using a 5/8" spark plug socket, 3/8" ratchet, and the needed 3/8" extension set.
• If access is angled, add a 3/8" swivel adapter.

Step 5: Install the new top spark plug

• Start the new plug by hand using the 5/8" spark plug socket and a 3/8" extension (no ratchet at first) until it threads smoothly.
• Tighten with a 3/8" torque wrench (ft-lb capable): Torque to 18 Nm (13 ft-lbs).
• Do not over-tighten (that can damage the aluminum cylinder head).

Step 6: Replace the second spark plug on the same cylinder (side plug)

• Locate the second plug boot/wire on the side of the cylinder head for that same cylinder.
• Pull the boot off by twisting and pulling (do not yank the wire).
• Blow out around the plug using a compressed air blow gun.
• Remove and install the side plug using a 5/8" spark plug socket, 3/8" ratchet, 3/8" extension set, and 3/8" swivel adapter as needed.
• Tighten with a 3/8" torque wrench (ft-lb capable): Torque to 18 Nm (13 ft-lbs).

Step 7: Reinstall the coil and boot

• Apply a small dab of dielectric grease inside the coil boot.
• Reinstall the coil onto the top plug.
• Install the coil bolt using a 10mm socket, then tighten with a 3/8" torque wrench (ft-lb capable): Torque to 12 Nm (105 in-lbs).
• Reconnect the coil electrical connector until it clicks.
• Reinstall the side plug boot fully until it seats.

Step 8: Repeat for all cylinders

• Repeat Steps 3–7 for each cylinder, one at a time, to avoid mixing up connectors/boots.
• Rear cylinders need patience and a swivel.

Step 9: Reassemble and reconnect the battery

• Reinstall the engine cover by pressing it down evenly by hand.
• Reconnect the negative battery cable using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 30–60 seconds.
• Listen/feel for a misfire (shaking) and verify the check engine light stays off.
• If you get a misfire right after the job, re-check that every coil connector is fully clicked in and every plug boot is fully seated.
• One loose connector can mimic bad plugs.

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💰 DIY vs Shop Cost

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

DIY Cost: $120-$260 (parts only)

You Save: $330-$640 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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