Subaru Outback Misfire Fix (2000–2004 EJ25) – Spark Plug Replacement Guide

For a few months now, I’ve gotten the occasional check engine light on my 2001 Outback. Every time, it was a code for a misfire in cylinder 1. I’d reset it and be on my way, until it would reappear a couple weeks later. It was time to investigate.

Causes of Subaru Misfires

There are many potential causes of an engine misfire, but one of the most common, easiest and cheapest to fix are the spark plugs. The wrong spark plug can cause all kinds of problems–rough running, poor acceleration, poor fuel economy, and misfires.

I picked up a set of NGK V-Power copper spark plugs. These are the same type used from the factory and what the engineers intended. The downside is copper plugs require more frequent changes. That wasn’t a problem for me–just means more wrenching.

Changing the Spark Plugs

Changing the spark plugs on a 2000-2004 Subaru Outback with the EJ25 engine is a pretty simple task. Space is tight on the driver’s side, but removing the air box and hoses gives you all the room you need on the passenger side.

Even if you’ve never done it before, you should be able to change all the plugs in under an hour.

1. Make sure the engine is cool before working. Take all proper safety precautions.
2. Remove the air box and hoses with a 10mm and 12mm socket.
3. Remove the passenger side spark plugs with a ⅝ spark plug socket, ratchet and extension.
4. Make sure the new plugs are gapped properly at .040”. A feeler gauge is a handy tool to have for this task. Do not use anti-seize.
5. Install the spark plugs on the passenger side. Hand tighten the plugs, then give them a 1/2 turn with your ratchet.
6. Put the spark plug wires back on the plugs. I decided this was a good time to upgrade to NGK spark plug wires.
7. Repeat the process on the driver’s side, working around the battery and windshield washer fluid reservoir. 
8. Replace the air box and hoses.
9. Go for a test drive!

The Verdict

I cleared the check engine light code again and started it up. Immediately, it ran much smoother and lacked the rough idle on startup that it had before. On the test drive, the Subaru accelerated better and the “seat of your pants” feel was much smoother and quicker. In all, this fix cost me less than $20 (excluding the optional spark plug wires) and the car runs much better.

The lessons here:

1. Use manufacturer-recommended parts. “Newer” or “upgraded” doesn’t always mean better.
2. Start with the low-cost fixes first, before investing time and money unnecessarily.

If your Subaru is running rough or throwing a misfire code, try swapping in OEM-style plugs before tackling bigger repairs. This quick fix worked for me, and it might save you time and money, too.

Heads up: a few links here may be affiliate links. Using them supports Fix Up Fleet without costing you extra — and lets me buy the next batch of parts for new projects.