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2003 Honda Civic EX (~230,000 miles) has been giving me misfire codes for a while, mostly on cylinders 2 & 3, but sometimes 4.

  • P0300 Random cylinder
  • P0302 Cylinder 2
  • P0303 Cylinder 3
  • P0304 Cylinder 4

Took it to mechanic and they couldn't figure out what's wrong, they see the codes, too, but didn't see/hear any misfires, and said I should keep driving it and see if it gets worse and then it will be easier to identify. Any advice on how to identify the cause? (It has P0420 catalytic converter code for a long time, too. We've pretty much given up on fixing that.)

  • No idea what the misfire rate is? How fast does a misfire come back after you clear the code? – Pᴀᴜʟsᴛᴇʀ2 Jan 24 '18 at 17:47
  • Also, considering this is a VTEC engine, there may be issues starting to appear with the system. Double check oil level. Ensure oil has been changed on time. – Pᴀᴜʟsᴛᴇʀ2 Jan 24 '18 at 18:20
  • @Pᴀᴜʟsᴛᴇʀ2 code comes back on within a few days of clearing it. Oil level is good as of a few days ago – endolith Jan 24 '18 at 18:33
  • What shape are the spark plugs in? Pull a few and check them out. – SteveRacer Jan 25 '18 at 2:58
  • @SteveRacer They're new; they were replaced the first time it took it in for this. – endolith Jan 25 '18 at 4:40
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You can do what the mechanic should have done and test the cylinder balance, ignition, injection and compression to fully diagnose the misfire.

Use this guide as a reference, its fairly comprehensive and specific to your vehicle as far as I can tell. http://troubleshootmyvehicle.com/honda/1.7L/how-to-test-misfire-codes-2

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