The Subaru Ascent uses a modern engine layout that places spark plugs under the hood in accessible but tight spaces. Understanding exact locations and replacement steps helps owners perform maintenance efficiently and avoid damage. This guide focuses on the Ascent’s common FA24 2.4L turbo engine and outlines where to find the spark plugs, how to access them, and practical replacement tips for U.S. models.
Location Of Spark Plugs On Subaru Ascent
The Subaru Ascent with the FA24 2.4L turbocharged flat-four engine uses four ignition coils and four spark plugs. The ignition coils sit on top of each cylinder bank, mounted per cylinder directly over the spark plug wells. In practical terms, the spark plugs are located under the coil packs on the cylinder heads, near the valve covers. Access is from the top side of the engine bay, not from underneath the vehicle. The plugs are positioned in the center of each bank, making them far more accessible than some transverse engines, but space is still tight due to the horizontal layout and wiring harness routing. Always refer to the owner’s manual for exact torque specifications and plug gap requirements.
Access And Replacement Steps
Before starting, gather the right tools and follow safety precautions. The replacement interval for Subaru Ascent spark plugs is typically around 60,000–100,000 miles depending on fuel, driving conditions, and plug type. For the FA24 engine, OEM or equivalent air-fuel-efficiency plugs are recommended. The steps below assume you are replacing all four plugs with the proper gap and heat range.
- Prepare the vehicle: Park on a flat surface, engage the parking brake, and disconnect the negative battery terminal to prevent any electrical shorts.
- Gain access to the coils: Remove engine cover if equipped, then locate the four ignition coils on top of the engine. The coils sit directly above each spark plug well. Disconnect the electrical connectors from each coil and carefully remove the coil packs using the correct size socket or screwdriver as required by the model year.
- Remove the old spark plugs: With the coils removed, use a spark plug socket with a swivel adapter to reach each plug. Carefully thread counterclockwise to break the seal, avoiding sudden twists that could damage the cylinder head or threads. Gently lift the plug out straight to prevent cross-threading.
- Check plug gapping: Inspect each plug’s gap and reset to the manufacturer’s specification if needed. A common gap for Subaru engines is around 0.028–0.032 inches, but verify with the owner’s manual or a trusted source for the exact FA24 specification.
- Install new plugs: Thread the new plugs by hand to avoid cross-threading, then tighten to the specified torque using a torque wrench. Over-tightening can strip threads, while under-tightening can cause poor sealing and misfires.
- Reinstall coils and wiring: Reinsert each ignition coil, reconnect the electrical harness, and snug the coil bolts to the specified torque. Ensure the coil boots seal properly against the spark plug wells to prevent moisture ingress.
- Reassemble: Refit the engine cover if removed. Reconnect the battery, start the engine, and listen for any misfires or rough running, indicating a misinstalled plug or coil.
Tools, Parts, And Safety Considerations
Having the right tools speeds up the process and reduces the risk of damage. Typical items include a spark plug socket (7/8 inch or as specified for the plug size), a torque wrench, a swivel extension, a ratchet, and an appropriate extension for reach. A diagnostic light or scan tool can help verify there are no trouble codes after replacement. Use anti-seize compound on new plugs only if recommended by the manufacturer; some brands discourage it as modern plugs can be installed dry with adequate torque. Follow all safety steps, including disconnecting the battery and allowing the engine to cool before starting.
Maintenance Best Practices
Proper maintenance helps sustain engine performance and fuel efficiency. Regular inspection of ignition coils, plug wires (where applicable), and coil boots should accompany plug replacement. If the engine exhibits misfires, rough idling, decreased power, or increased fuel consumption, a plug replacement or coil check may be warranted. For high-mileage Ascent models, consider inspecting the coil boots for cracking or hardening, as deteriorated boots can cause misfires even with new plugs installed. Adhere to Subaru’s recommended service intervals and use OEM or OEM-equivalent spark plugs for best results.
Common Questions About Subaru Ascent Spark Plugs
Owners frequently ask about accessibility, replacement difficulty, and whether to use iridium, platinum, or copper plugs. In general, Subaru recommends using the correct heat range and gap for the FA24 engine. Iridium or platinum plugs can extend service life, but always confirm compatibility with the engine control unit and manufacturer guidance. If space or tool access is limited, some technicians use specialized extension tools or a magnetic pick-up to seat plugs properly. For those who prefer at-home maintenance, setting aside a dedicated 2–3 hour window ensures careful work without rushing the job.
Diagnostics And When To Seek Help
After replacing spark plugs, run the engine and monitor performance. If misfires persist, use a scan tool to check for misfire codes by cylinder. A misfire code alongside rough running can indicate a faulty coil, improper plug seating, or a damaged boot. In some cases, multiple control modules may need a reset or update to ensure proper fuel and ignition timing. If unsure about torque specs, plug gap, or coil compatibility, consult a certified Subaru technician to avoid potential engine damage.
Summary Of Key Points
- Location: Spark plugs reside under the ignition coils on top of the engine’s cylinder heads in the FA24 engine.
- Replacement interval: Typically 60,000–100,000 miles depending on plugs and conditions.
- Access approach: Remove the engine cover, detach coils, extract plugs with a swivel socket, verify gap, install new plugs to spec, and reseat coils.
- Safety: Disconnect battery, allow engine to cool, and use proper torque.