🔧 Grand Cherokee - Spark Plug Replacement

Your Grand Cherokee’s 6.4L HEMI uses 16 spark plugs (two per cylinder). Replacing them restores smooth idle, strong acceleration, and helps prevent misfires under load.

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

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⚠️ Safety & Precautions

• ⚠️ Work on a completely cool engine to avoid burns and damaged threads.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils.
• ⚠️ Keep dirt out of the plug holes—debris can damage the engine.
• ⚠️ Do not over-tighten spark plugs; stripped aluminum threads are expensive to fix.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 10mm wrench
• 3/8" drive ratchet
• 3/8" drive extensions (3", 6", 10")
• 3/8" drive swivel joint
• 5/8" (16mm) spark plug socket
• Torque wrench (ft-lb range)
• Torque wrench (in-lb range)
• Flat trim tool
• Small pick tool
• Compressed air blow gun
• Feeler gauge (inch)
• Dielectric grease
• Nitrile gloves
• Safety glasses
• Magnetic pickup tool

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (6.4L HEMI, two per cylinder) - Qty: 16
• Throttle body/intake tube clamp (optional if yours is damaged) - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and let the engine fully cool.
• Disconnect the negative battery terminal using a 10mm wrench.
• Lay out 16 new plugs in order so you can track progress.
• A spark plug socket is a deep socket with a rubber insert that grips the plug so it won’t fall out.
• A torque wrench clicks when you hit the correct tightness so you don’t strip threads.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull up firmly at the corners to pop the cover off (use a flat trim tool if needed).
• Set it aside where it won’t get scratched.

Step 2: Make room at the front if needed

• If access feels tight, loosen the intake tube clamps using a flat screwdriver (or the appropriate driver for your clamps), then lift the tube enough to reach the front coils.
• Take a quick photo before removing hoses.

Step 3: Unplug one ignition coil (do one plug at a time)

• Pick one cylinder and start there so nothing gets mixed up.
• Release the coil connector lock with a small pick tool, then unplug the connector by hand.

Step 4: Remove the ignition coil

• Remove the coil mounting bolt using a 10mm socket and 3/8" ratchet.
• Twist the coil slightly, then pull it straight up to remove it.
• When reinstalling the coil bolt later: Torque to 5 Nm (44 in-lbs).

Step 5: Clean the spark plug well

• Blow out the plug hole using a compressed air blow gun while wearing safety glasses.
• This helps prevent dirt from falling into the cylinder when the plug comes out.

Step 6: Remove the old spark plug

• Use a 5/8" (16mm) spark plug socket with a 3/8" ratchet and the needed extensions (add a swivel joint if the angle is tight).
• Turn counterclockwise and lift the plug out with the socket.
• If the plug feels stuck, stop and work it gently—don’t force it.

Step 7: Check and prepare the new spark plug

• Check the gap with a feeler gauge (inch); target is typically 0.043 in (1.1 mm) for the 6.4L.
• If your new plugs are iridium/platinum, avoid bending the fine center electrode.
• Do not apply anti-seize unless the plug manufacturer specifically requires it (most modern plugs are coated).

Step 8: Install the new spark plug

• Thread the new plug in by hand using the spark plug socket and a short extension only (no ratchet at first).
• Once it seats, tighten using a torque wrench (ft-lb range): Torque to 18 Nm (13 ft-lbs).
• If it won’t hand-thread, back out and retry.

Step 9: Reinstall the coil

• Apply a tiny dab of dielectric grease inside the coil boot.
• Push the coil straight down until it fully seats on the plug.
• Install the coil bolt using a 10mm socket, then use a torque wrench (in-lb range): Torque to 5 Nm (44 in-lbs).
• Reconnect the electrical connector until it clicks/locks.

Step 10: Repeat for all remaining plugs

• Repeat Steps 3–9 for each coil/plug location.
• Use a 3/8" swivel joint and longer extensions for the rear cylinders near the firewall.
• If you drop anything, retrieve it with a magnetic pickup tool before continuing.

Step 11: Reassemble and reconnect the battery

• Reinstall any intake tube/hoses you moved and tighten clamps using the same driver you used to loosen them.
• Reinstall the engine cover by lining up the grommets and pressing down firmly.
• Reconnect the negative battery terminal using a 10mm wrench.

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✅ After Repair

• Start the engine and let it idle for 1–2 minutes; it should run smooth with no shaking.
• Check for a blinking check engine light (that indicates an active misfire—shut it off and recheck coil connectors).
• Take a short test drive and verify normal power and no fuel smell.
• If a check engine light stays on, scan for codes (often a loose coil connector).

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💰 DIY vs Shop Cost

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

DIY Cost: $160-$320 (parts only)

You Save: $290-$580 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?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.