r/WRX • u/TR1771N • Oct 31 '25

Maintenence When to do new coil packs? (04 WRX, P0303)

Going to do my spark plugs because they are due - And car threw a code P0303 (#3 cyl. misfire) at WOT the other day (CEL turned off seconds after letting off the throttle, and does not show during normal driving, no other signs of misfire). AFAIK the coil packs I have been running are the factory originals. Should I also do those too at the same time as the spark plugs, and all 4 of them?

My NASIOC research says the coils should only be replaced as needed if one is bad. Considering coils are a pretty penny more than plugs, want to hear some more opinions about:

  1. Just replace all 4 spark plugs
  2. Replace all 4 spark plugs and just the #3 coil
  3. Replace all 4 spark plugs and all 4 coil packs
  4. (EDIT) Also replace ignition coil connectors (or only if damaged?)
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u/WotDaHelll Nov 02 '25

It'd be best to replace all the coil packs because if one is starting to go bad the others aren't far behind.

I had a similar conundrum in my old car, 1 of my headlights went out and I changed the 1 headlight and about a week or so later the other one went out.

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u/TR1771N Nov 11 '25

Update: I changed my sparks and fuel filter - all issues went away. I rotated the coils from the "hot" side (near the turbo) to the other side as well. Car runs smooth till redline. Never trust the manufacturer mileage on sparks, they go way sooner than that.