Misfiring under boost

[drifter001]

Not sure if I’m posting in the right spot so mods please feel free to move as needed.

I’ve got a 05 wrx that’s been tuned by a reputable shop. Lately I’ve had an issue where I get a misfire code from a single cylinder. Upon further examining, I noticed that it happens after passing about 5psi boost. My initial thought was maybe a bad coil pack but after paying more attention to my boost, I’m thinking that may not be it. Any suggestions on where to start?

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[Brock31]

Move the coil pack to another cylinder and see if the misfire moves to that cylinder.

[Charlie-III]

Originally Posted by Brock31

Move the coil pack to another cylinder and see if the misfire moves to that cylinder.

Agreed.
The coilpack, or maybe spark plug, may be weak/failing. Boost makes it harder for the spark to jump the gap leading to a missfire. If moving the coilpack makes no difference, swap the plug.

[drifter001]

Thanks for the suggestion. I'll give that a shot

[drifter001]

So the codes that I’m getting are P0302 and P0304

[Charlie-III]

Originally Posted by drifter001

So the codes that I’m getting are P0302 and P0304

So, misfire on cylinders 3&4.

But, you originally stated a single cylinder misfire. Is this getting worse? Have you swapped parts to see if issue follows a part?

[drifter001]

Originally Posted by Charlie-III

So, misfire on cylinders 3&4.

But, you originally stated a single cylinder misfire. Is this getting worse? Have you swapped parts to see if issue follows a part?

The original code was p0302. I swapped parts on the same bank so 2 and 4 if I got my firing order right and now I got p0302 and P0304

[Charlie-III]

Originally Posted by drifter001

The original code was p0302. I swapped parts on the same bank so 2 and 4 if I got my firing order right and now I got p0302 and P0304

So, could be a bad #2 coil and plug. When you swapped, you moved part of the issue to #4, but still have bad plug in #2. The plug could be fouled by bad coil.

[drifter001]

Originally Posted by Charlie-III

So, could be a bad #2 coil and plug. When you swapped, you moved part of the issue to #4, but still have bad plug in #2. The plug could be fouled by bad coil.

So I should try replacing plug in #2 cylinder and see if it at least that code clears then try for the #4 coil pack?

[Charlie-III]

Originally Posted by drifter001

So I should try replacing plug in #2 cylinder and see if it at least that code clears then try for the #4 coil pack?

Sure, it would help diagnosis, on both counts.

What is the mileage on the plugs now and what are they? If old/high mileage, may be time for 4 new plugs.

[drifter001]

Originally Posted by Charlie-III

Sure, it would help diagnosis, on both counts.

What is the mileage on the plugs now and what are they? If old/high mileage, may be time for 4 new plugs.

I’d say they’re about 20-30k old. They’re the OEM plugs purchased from the subie dealership

[drifter001]

Originally Posted by Charlie-III

Sure, it would help diagnosis, on both counts.

What is the mileage on the plugs now and what are they? If old/high mileage, may be time for 4 new plugs.

So replaced coil pack in #2 cylinder and now I’m getting a p0304 and misfiring starts at over 5psi still. Is it possible that overall health of my coil packs is deteriorating or am I chasing something that may not be an issue?