Random Misfire codes?

Tiny
GOTTAKEEPMOVIN'
  • MEMBER
  • 2010 HYUNDAI ACCENT
  • 1.6L
  • 4 CYL
  • AUTOMATIC
  • 54,000 MILES
Misfiring and CEL upon starting car this morning. Codes P0300, P0303, and P0304 were present. Swapped out coil packs (#1 and #3) and (#2 & #4). Codes were then P0300, P0301, and P0303, which didn't quite make sense. Re-assembling in original positions gives only a P0303 failure now. Upon R&R of coil packs, I noticed cracks on 3 of the 4 coil packs (see pics) Although they show no sign of carbon or sparking happening at this crack, it surely can't be good. Spark plugs were all dry and tight. I am considering replacing all 4 coil packs. Can you recommend anything I have missed? Many Thanks!
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Monday, January 5th, 2026 AT 10:41 AM

6 Replies

Tiny
GOTTAKEEPMOVIN'
  • MEMBER
  • 45 POSTS
Close-up of crack
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Monday, January 5th, 2026 AT 10:43 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,397 POSTS
I suspect you got to them before they showed obvious carbon tracking. When you started it cold any condensation in the plug wells would be conductive and would have made the misfires occur. Then you swapped them back and they had run enough that they had dried out and stopped missing. I would change all of them as the last one isn't likely going to last much longer. 15 years on OEM coils isn't that bad, especially when you look at the plastic they made things out of then. OE on those was made by Denso so I'd get either Denso or Hitachi as replacements.
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Monday, January 5th, 2026 AT 11:08 AM
Tiny
GOTTAKEEPMOVIN'
  • MEMBER
  • 45 POSTS
I agree! Thanks so much!
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Monday, January 5th, 2026 AT 11:11 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,475 POSTS
STEVE W. Is one of our best! Please let us know what happens.
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Wednesday, January 7th, 2026 AT 11:07 AM
Tiny
GOTTAKEEPMOVIN'
  • MEMBER
  • 45 POSTS
Yes indeed. The failures were random but I got the faults down to a single P0303. Bought a 4-pack of plug coils and replaced the #3 first. Problem was solved. I replaced the other 3, in advance of further failure. Been running like a top for the last day with no further codes! Thanks so much!
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Wednesday, January 7th, 2026 AT 11:51 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,397 POSTS
You are welcome.
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Wednesday, January 7th, 2026 AT 5:45 PM

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