🔧 MX-5 Miata - Spark Plug Replacement

Replacing spark plugs on your MX-5 Miata restores strong ignition, smooth idle, and good fuel economy. This job is straightforward because the plugs are on top of the engine under the ignition coils.

Difficulty Level: Beginner | Estimated Time: 0.8-1.5 hours

---

⚠️ Safety & Precautions

• 🔥 Work on a fully cool engine to avoid burns and prevent thread damage in the aluminum cylinder head.
• 🧯 Keep dirt out of the spark plug holes; debris can damage the engine.
• 🔋 Battery disconnect is not required, but avoid touching metal tools across electrical connectors.

---

🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 3/8" ratchet
• 3/8" extension set (3" and 6")
• 14mm thin-wall spark plug socket (magnetic or rubber insert)
• Torque wrench (3/8", 5-60 Nm range)
• Plastic trim tool
• Compressed air blow gun

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (OEM-spec iridium) - Qty: 4
• Dielectric grease - Qty: 1

---

📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool completely (at least 1 hour).
• Have compressed air ready to blow out each spark plug well before removing the plug.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Use a plastic trim tool and your hands to lift the cover straight up (it pulls off grommets).

Step 2: Unplug the ignition coil connectors

• There are 4 ignition coils on top of the engine (one per cylinder).
• Use a plastic trim tool to gently lift the connector lock tab (if tight), then pull the connector straight off.
• Don’t pull on the wires.

Step 3: Remove the ignition coils

• Use a 10mm socket with a 3/8" ratchet to remove each ignition coil hold-down bolt.
• Pull the coil straight upward to remove it.
• Set coils in order (so they go back in the same cylinders).

Step 4: Clean the spark plug wells

• Use compressed air blow gun to blow out dirt around each spark plug.
• This prevents grit from falling into the engine.

Step 5: Remove the old spark plugs

• Use a 14mm thin-wall spark plug socket, 3/8" extension, and 3/8" ratchet to loosen and remove each plug.
• If a plug feels extremely tight, stop and re-check the socket is fully seated straight.

Step 6: Install the new spark plugs

• Confirm the new plugs are OEM-spec iridium and do not adjust the gap (iridium tips can be damaged).
• Start each plug by hand using the spark plug socket and extension only (no ratchet) to avoid cross-threading.
• Once finger-tight, use a torque wrench to tighten: Torque to 15-20 Nm (11-15 ft-lbs).
• No anti-seize on plated plugs.

Step 7: Reinstall coils and connectors

• Apply a very small amount of dielectric grease inside each coil boot.
• Push each coil straight onto the spark plug until fully seated.
• Use a 10mm socket and torque wrench to tighten coil bolts: Torque to 8-10 Nm (71-89 in-lbs).
• Reconnect each coil connector until it clicks/locks.

Step 8: Reinstall engine cover

• Align the cover with the grommets and press down firmly by hand.

---

✅ After Repair

• Start the engine and let it idle for 30-60 seconds; it should run smooth with no shaking.
• If you get a check engine light or rough running, shut it off and re-check each coil connector is fully clicked in.
• Take a short test drive, then re-check for any abnormal smell or sounds.

---

💰 DIY vs Shop Cost

Shop Cost: $220-$400 (parts + labor)

DIY Cost: $60-$140 (parts only)

You Save: $160-$260 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.8-1.2 hours.

---

🎯 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.