🔧 Flex - Spark Plug Replacement

On your Flex, the spark plugs sit under ignition coils (one coil per plug). The front bank is straightforward; the rear bank usually requires removing the upper intake manifold so you can reach the plugs safely without damaging anything.

Difficulty Level: Intermediate | Estimated Time: 2.5-4.5 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a cool engine to avoid burns and thread damage in the cylinder head.
• ⚠️ Keep dirt out of the engine: cover intake openings immediately after removing the intake manifold.
• ⚠️ No smoking/open flames—fuel vapors can be present around the intake.
• ⚠️ Disconnect the negative battery cable if you’ll be unplugging multiple connectors for the intake (recommended).

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🔧 Required Tools

You'll need the following tools for this repair:

• 8mm socket
• 10mm socket
• 7mm socket
• 1/4" drive ratchet
• 3/8" drive ratchet
• 3/8" drive torque wrench (10–30 ft-lbs range)
• 1/4" drive torque wrench (in-lb torque wrench)
• 3/8" drive extension set (3" and 6")
• 5/8" spark plug socket
• Pick tool
• Flathead screwdriver
• Needle-nose pliers
• Trim clip removal tool
• Compressed air blow gun
• Shop vacuum
• Masking tape and marker
• Clean rags
• Dielectric grease
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (OEM equivalent, correct heat range) - Qty: 6
• Upper intake manifold gasket set - Qty: 1
• Throttle body gasket - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and let the engine cool fully.
• Use masking tape and marker to label any hoses/connectors you remove. It prevents “where does this go?” later.
• Disconnect the battery: use a 10mm socket to remove the negative (-) cable and move it aside.
• Assumption: rear plugs require upper intake manifold removal (common on the 3.5L transverse layout).

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover and open up access

• Pull up to remove the decorative engine cover (it’s usually held by grommets).
• Use a trim clip removal tool as needed so you don’t crack plastic clips.

Step 2: Remove the air intake tube (to make room)

• Use a 7mm socket to loosen the hose clamps on the intake tube.
• Unplug any sensors on the tube by pressing the tab; use a pick tool gently if the lock is stubborn.
• Remove the intake tube and set it aside.

Step 3: Replace the front-bank spark plugs (front of engine)

• Unplug one ignition coil connector at a time (press the tab, then pull).
• Remove the coil hold-down bolt using an 8mm socket.
• Twist the coil boot slightly, then pull the coil straight up and out.
• Blow out the spark plug well using compressed air blow gun so debris can’t fall into the cylinder.
• Remove the spark plug using a 5/8" spark plug socket, 3/8" drive ratchet, and extension.
• Install the new plug by lowering it in with the spark plug socket and turning it by hand first (this prevents cross-threading).
• Tighten with a 3/8" drive torque wrench: Torque to 15 Nm (11 ft-lbs).
• Apply a small dab of dielectric grease inside the coil boot (dielectric grease is a non-conductive grease that helps prevent moisture and future sticking).
• Reinstall the coil and bolt with an 8mm socket: Torque to 7 Nm (62 in-lbs).
• Reconnect the coil connector until it clicks.
• Repeat for the other front-bank cylinders.

Step 4: Remove the upper intake manifold (to reach the rear plugs)

• Unplug the throttle body connector and any intake-related connectors you can see; use a pick tool carefully for locking tabs.
• Disconnect small vacuum/PCV hoses using needle-nose pliers as needed (move clamps back first).
• Remove the upper intake manifold bolts using a 10mm socket and ratchet.
• Lift the upper intake manifold off gently. If it sticks, use a flathead screwdriver very carefully at a reinforced edge—do not gouge the sealing surfaces.
• Immediately cover the intake openings with clean rags to keep bolts/dirt out of the engine.

Step 5: Replace the rear-bank spark plugs (rear of engine)

• Remove each rear ignition coil: unplug connector, then use an 8mm socket to remove the coil bolt.
• Blow out each plug well using the compressed air blow gun.
• Remove each plug using a 5/8" spark plug socket, extension, and 3/8" drive ratchet.
• Install each new plug by hand first, then torque: Torque to 15 Nm (11 ft-lbs).
• Add a small amount of dielectric grease inside each coil boot, reinstall coils, and tighten coil bolts: Torque to 7 Nm (62 in-lbs).
• Reconnect each coil connector until it clicks.

Step 6: Reinstall the upper intake manifold with new gaskets

• Remove old intake manifold gaskets. Clean the mating surfaces using clean rags (no scratching).
• Install the new upper intake manifold gaskets.
• Set the upper intake manifold back in place.
• Install bolts finger-tight first using a 10mm socket, then tighten evenly in a crisscross pattern.
• Tighten with a 1/4" drive torque wrench (in-lb torque wrench): Torque to 10 Nm (89 in-lbs).
• If the throttle body was removed, install a new throttle body gasket and tighten fasteners evenly: Torque to 10 Nm (89 in-lbs).
• Reconnect all hoses and electrical connectors.

Step 7: Reinstall the intake tube and engine cover

• Reinstall the air intake tube and tighten clamps using a 7mm socket.
• Reconnect any sensors you unplugged (listen for the click).
• Press the engine cover back onto its mounts.

Step 8: Reconnect battery

• Reconnect the negative battery cable using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 1–2 minutes. It should run smooth with no shaking.
• Listen for hissing (vacuum leak). If you hear it, re-check intake hoses and manifold seating.
• Road test 10–15 minutes, then re-check for any warning lights.
• Tip: If a check engine light appears, a connector is often not fully clicked in.

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💰 DIY vs Shop Cost

Shop Cost: $350-$650 (parts + labor)

DIY Cost: $60-$160 (parts only)

You Save: $190-$590 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2.5-4.5 hours.

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🎯 Ready to get started?

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