Is it hard to change spark plugs on a Subaru WRX?

Not unduly hard, but it’s a mid-level DIY job that varies by model year and engine. With the right tools and careful steps, you can do it at home, though newer WRX engines place plugs deeper in the head and often require removing the intercooler and intake components. Plan for some time and patience, especially if you’re new to this task.

Why the effort varies by engine

Subaru’s WRX lineup has shifted across generations from the EJ-series engines to the turbocharged FA-series powerplants. The older EJ25 engines offered relatively straightforward access, while the newer FA20DIT and FA24DIT turbo engines place spark plugs in tight spaces with coil-on-plug ignition. Access is typically easier on the driver’s side, but the passenger-side rear plugs often require removing parts like the intercooler or associated piping. This mix of layouts is what makes the job feel easy to some and challenging to others, depending on the exact engine and your drivetrain configuration.

Engine generations at a glance

To give a sense of the difficulty, here’s how access tends to break down by typical WRX engines:

• EJ25 (older WRX models, approximate 2002–2014): Generally more accessible from the top; many owners report straightforward coil removal and plug replacement with moderate disassembly.


• FA20DIT (2015–2021 WRX): More cramped, with coil-on-plug ignition. Access to rear plugs often requires removing the intercooler and related intake components.


• FA24DIT (2022–present WRX): Similar in layout to the FA20 but with revisions; rear-bank access remains the tricky part, typically needing intercooler/piping removal and careful reassembly.

In practical terms, the job tends to be easiest when the intercooler and intake piping can stay in place, and hardest when you must remove multiple components to reach the rear plugs. Always consult the specific service manual for your exact model year and engine code before starting.

Tools, parts, and prep you’ll likely need

Preparing the right tools and parts helps ensure a smooth job. This list focuses on the common needs for modern WRX engines, though you should verify exact requirements for your model year.

• New spark plugs (NGK or Denso equivalents recommended by Subaru for your engine; ensure correct heat range and gap per manual)


• Spark plug socket (typically 5/8 inch) with a long extension and a wobble/swivel adaptor


• 3/8 inch drive ratchet, long-reach extensions (6–12 inches) to reach tight spots


• Torque wrench capable of precise low-range torque (roughly 13–16 ft-lb / 18–22 Nm is a common target; check the service manual)


• Dielectric grease for coil boots


• Magnetic pickup/tool or similar to retrieve dropped sockets


• Screwdrivers and pliers for hose/clamp removal


• Shop towels and a coolant-safe container for any incidental spills


• Gloves and eye protection


• Optional: gap gauge to verify or adjust plug gaps if using non-pre-gapped plugs

Note: Do not over-tighten spark plugs and follow Subaru’s guidance on anti-seize application. Modern iridium/platinum plugs often ship pre-gapped and do not require anti-seize; using it can lead to over-torquing and thread distortion.

Step-by-step approach to replacing spark plugs

Here is a general sequence that fits the common WRX engine layouts. The exact steps can vary by model year and whether you need to remove the intercooler or intake piping to access the rear plugs.

1. Prepare the vehicle: Park on a level surface, engine cold, disconnect the negative battery terminal to avoid any accidental electrical shorts.


2. Gain access: Remove the necessary components to reach the spark plugs. On FA20/FA24 engines this usually means removing the intercooler and associated intake tubing; on older EJ engines you may only need to lift the engine cover and clear space above the plugs.


3. Identify and remove coil packs: Unplug the ignition coil connectors, unbolt or unclip each coil pack, and set them aside in a safe area. Do one bank at a time to avoid mixing up components.


4. Remove old plugs: Use the spark plug socket with the proper extension to reach each plug. Carefully loosen and remove the old plugs, keeping the area clean to prevent debris from falling into the cylinder.


5. Inspect and gap new plugs: If the plugs aren’t pre-gapped, use a gap tool to set the correct clearance per Subaru’s specification for your engine. Clean debris from the plug wells before installing.


6. Install new plugs: Thread in by hand to avoid cross-threading, then snug with a torque wrench to the spec in your manual (common range is about 13–16 ft-lb; do not over-tighten).


7. Reinstall coils and wiring: Reconnect each coil pack to its corresponding plug, re-seat the hoses and intercooler/piping if removed, and secure all clamps and connections.


8. Reconnect and test: Reconnect the battery, start the engine, and listen for any misfires or unusual noises. If anything sounds off, double-check coil connections and plug seating.

Replacing spark plugs on a WRX is not a routine maintenance item for beginners, but with careful planning and methodical work, it’s a repeatable DIY task. If you’re unsure at any point, consult a service manual for your exact year and engine code or seek professional help.

Tips, caveats, and best practices

These pointers can help reduce frustration and avoid common mistakes during a plug change on a WRX.

• Make a small diagram or label each coil and plug position to prevent mounting mismatches after reassembly.


• Work in a clean, well-lit area to prevent debris from entering once the plugs are exposed.


• On FA-series engines, removing or loosening the intercooler is often the fastest way to reach the rear plugs; plan this step ahead of time.


• Do not reuse old coil boots if they show cracks or deformation; replace as needed to maintain proper ignition seal.


• After completing the job, clear any error codes by disconnecting the battery for a few minutes or by using an OBD-II scanner if available.

While the job can be done at home, consider the time commitment. It’s common for a first-timer to spend 2–4 hours, depending on engine variant and how comfortable you are with vehicle disassembly and reassembly.

Summary

Changing spark plugs on a Subaru WRX is a manageable challenge that hinges on engine design. Older EJ25 engines are relatively friendlier, while FA20 and FA24 turbo engines introduce tighter access and the need to remove the intercooler to reach the rear plugs. With the right tools, a careful plan, and attention to torque specifications, you can complete the job at home. Always verify exact procedures and torque values in your vehicle’s service manual for your model year to ensure accuracy and safety.