🔧 WRX - Spark Plug Replacement

Replacing spark plugs on your WRX helps keep it starting easily, idling smooth, and making full power under boost. On your WRX, the plugs sit on the sides of the engine, so we make room by removing a few intake/intercooler parts and then swapping the plugs one cylinder at a 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 thread damage in the aluminum cylinder heads.
• ⚠️ Do not drop anything into the intake pipes or throttle body; cover openings with a clean rag.
• ⚠️ Pull the negative battery cable before removing the battery and before unplugging ignition coils.
• ⚠️ Never use anti-seize on modern plated spark plug threads unless the plug maker specifically says to; it can cause over-tightening.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Fender cover
• 3/8" drive ratchet
• 1/4" drive ratchet
• 3/8" drive torque wrench (10-30 ft-lbs range)
• 1/4" drive torque wrench (50-150 in-lbs range)
• 14mm thin-wall spark plug socket (3/8" drive)
• 3/8" drive 6" extension
• 3/8" drive wobble extension
• 3/8" drive universal joint
• 10mm socket (1/4" drive)
• 12mm socket (3/8" drive)
• 10mm wrench
• Flathead screwdriver
• Needle-nose pliers
• Spark plug gap gauge (wire-style)
• Compressed air blow gun
• Shop vacuum
• Work light

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (correct OEM-spec heat range for WRX) - Qty: 4
• Dielectric grease (small packet) - Qty: 1

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📋 Before You Begin

• Park on level ground, put the transmission in 1st gear, and set the parking brake.
• Let the engine cool completely (at least 1-2 hours after driving).
• Open the hood and disconnect the negative battery terminal using a 10mm wrench.
• Lay out the new plugs and check the gap with a wire-style gap gauge (don’t force the center electrode).

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the top-mount intercooler for room

• Loosen the intercooler hose clamps using a flathead screwdriver.
• Remove the bypass valve bolts using a 12mm socket.
• Remove intercooler mounting bolts using a 12mm socket.
• Carefully lift the intercooler up and out; cover open hoses with a clean rag. Take a quick photo for reassembly.

Step 2: Create side access (battery side and airbox side)

• Driver side: remove the battery hold-down using a 10mm socket, then lift the battery out (it’s heavy).
• Passenger side: loosen the intake/airbox clamps with a flathead screwdriver and remove the airbox/snorkel pieces as needed for hand room.

Step 3: Unplug and remove the ignition coil on cylinder you’re working on

• Locate the coil pack on the side of the engine.
• Press the connector lock and unplug the coil.
• Remove the coil retaining bolt using a 10mm socket.
• Twist the coil gently and pull it straight out.

Step 4: Clean the spark plug well before removing the plug

• Use a compressed air blow gun and/or shop vacuum to remove dirt around the plug hole.
• This helps prevent grit from falling into the cylinder.

Step 5: Remove the old spark plug

• Install the 14mm thin-wall spark plug socket with a 3/8" drive wobble extension and 3/8" drive ratchet.
• A wobble extension is an extension that flexes slightly to help reach bolts at a small angle.
• Break the plug loose slowly, then spin it out the rest of the way.

Step 6: Install the new spark plug (don’t cross-thread)

• Check the new plug gap with the wire-style gap gauge (match the plug maker spec for your WRX plug set).
• Start threading the new plug by hand using the spark plug socket and extension only (no ratchet at first) so you can feel it thread smoothly.
• Torque the spark plug using a 3/8" drive torque wrench: Torque to 21.6 Nm (15.9 ft-lbs).
• If you don’t have a torque wrench: tighten until the crush washer seats, then an additional small turn. Torque wrench is strongly recommended.

Step 7: Reinstall the ignition coil

• Put a small dab of dielectric grease inside the coil boot.
• Push the coil straight onto the plug until fully seated.
• Install the coil bolt using a 10mm socket: Torque to 10 Nm (7.4 ft-lbs).
• Reconnect the electrical connector until it clicks.

Step 8: Repeat for the remaining 3 cylinders

• Do one cylinder at a time so you don’t mix up connectors or hardware.
• Use the universal joint and wobble extension as needed for tight angles.

Step 9: Reinstall the intercooler, intake pieces, and battery

• Reinstall intake/airbox parts using a flathead screwdriver for clamps.
• Reinstall the battery and hold-down using a 10mm socket.
• Reconnect the negative battery terminal using a 10mm wrench.
• Reinstall the intercooler and all bolts using a 12mm socket.
• Tighten all intercooler hose clamps using a flathead screwdriver. Loose clamps cause boost leaks.

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✅ After Repair

• Start the engine and let it idle for 1-2 minutes; it should idle smoothly.
• Listen for hissing (intake/boost leak) around the intercooler couplers.
• Test drive gently first, then do a short pull; if it stumbles, recheck coil connectors and intercooler clamps.
• If you get a flashing check engine light (misfire), stop driving and recheck coil seating and plug torque.

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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 2-3 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.