Press "Enter" to skip to content

S401 Coil Swap

I must be a sucker for punishment, but hey, I’m getting really good at doing the plugs on the Legacy.

Even after installing new spark plugs the other day, the idle was still lumpy and it was down on power. I decided to pick up a set of good, used standard coils because after seeing the old plugs, I just did not trust that the coils were any good. Trying to push a spark over that gap would be enough to kill any coil.

The “new” coils arrived today, so I went to work smothering them in silicone sealant. It’s a good insulator, and helps keep the spark where it should be. I smeared a decent layer of it on the sides, making sure to cover all the seams. I didn’t want to be pulling these out again, for the third time, to do this later.

I also smeared Dielectric grease on the little bit on the coil that the rubber stem goes onto. This will also help keep the spark going to the plug.

Because I’m good at it now, I started by removing the RH side coils, and spark plugs. The coils look somewhat ok, dirty but no obvious cracks. One weird thing I noticed is that all my coils were grey, whilst the replacements were all black.

So the first three spark plugs all look similar. Slightly dark, but no deposits and an OK color.

But when I came to the front LH spark plug something was wrong.

This plug was installed at the same time as the others. No carbon at all. Nothing. It hasn’t ignited a damn thing. Its been running on exactly three cylinders this whole time.

Coincidentally, this is also the same cylinder that had a very wet plug when I removed the old plugs previously.

So I buttoned it all back up with the replacement coils and fired it up. I remembered to do the idle re-learn this time.

Verdict? Oh my gosh. It idles so smooth you can almost forget the engine is even running, and the power is insane. It’s so smooth, and it just pulls and pulls. I took it for a decent drive and I couldn’t stop grinning, it drives like no other Legacy I have ever driven.

The Primary turbo comes on at a twitch of the throttle, Valley of Death is nothing but a quick blip in the power and then the Secondary turbo is forcing you into your seat all the way to redline. The short ratio gears in the six speed keep it in the power band, not letting it drop out of the Secondary turbo range. Trips to the speed limit are stupidly rapid.

I now understand why STI built this car.

Now that it’s finally running right I can start to focus on other things, like the stereo and interior trim. It also deserves an oil change on the weekend.

Bonus image…. the leftovers from the cleaning in the weekend. I’ll need to water blast this, a broom didn’t touch it.

0 0 votes
Article Rating

Discover more from Tastes Like Petrol

Subscribe to get the latest posts to your email.

Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments