Engine code P0304 misfire

Tiny
THEGREATECB
  • MEMBER
  • 2005 CHEVROLET IMPALA
  • 3.8L
  • V6
  • 95,000 MILES
I have check engine light on. The code is P0304 which is a misfire on cylinder four. These cars have three coil packs that run two spark plugs on each coil. My question is, if it was a bad coil causing this problem, would it not be making two cylinders misfire instead of just one? Because each coil runs two spark plugs. Unless a coil can go bad and only mess up one cylinder?
Monday, March 12th, 2018 AT 10:29 AM

1 Reply

Tiny
STEVE W.
  • MECHANIC
  • 13,967 POSTS
Yes, a coil can go bad and misfire only one cylinder, but it is not as common as a bad wire or plug. The easy way to test that is to just flip the plug wires on the coil towers. If the misfire stays in number four you know it is a bad wire, plug or an injector or internal engine problem. My normal routine is to flip the wires, then pull the plug and check the compression in that cylinder. Once you are sure the compression is good then it is check the injector flow and activation. Then change the plugs and wires.
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Monday, March 12th, 2018 AT 11:49 AM

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