Sudden cylinder misfire? ?

(2009 Honda Accord Coupe V6) As I was arriving home and started backing into my driveway, my car began to idle very rough. First thing that came to mind was a cylinder misfire. I plugged in my OBD2 scanner and it confirmed my suspicions. Out came the code P0302. First thing I did was check all of the coil packs to see if they were getting a spark. They all passed the test. I decided to swap out spark plugs 2 and 4 with each other. The code scanner then gave me the code P0304 which made sense, but 302 stayed as well. I thought it would probably go away once I replaced the spark plug. I went to O’Reilys and got 2 spark plugs and swapped out 2 and 4. The problem persisted, only now, I’m also getting the code P0300 along with P0302 & P0304. What could be the cause of this? I was going to buy the other 4 spark plugs in hope that that would fix the issue but I wanted to ask for some expert help on this. It may or may not be worth mentioning that my engine had been running flawlessly smooth prior to this.

2 Answers

  • 1 month ago
    Favourite answer

    Honda's need the valves adjusted every 60,000 miles. They get tight and cause misfires, loss of power and a bad idle.

    Did you install NGK or Denso Iridium spark plugs? Those two are the only spark plugs that can be run in an Asian motor.

    Check the EGR valve to make sure it's clean of carbon which would keep it from closing and causing misfires.

    If you purchased gasoline recently take a gas sample in a glass jar. Fill it half full and after letting it sit for 20 minutes look for water in the bottom of the jar. Water might be the problem.

    If all those things are done and the misfire is still happening it's time to test the fuel pump pressure while driving the vehicle.

    Source(s): Mitsubishi Master Tech
  • Anonymous
    1 month ago

    "First thing I did was check all of the coil packs to see if they were getting a spark"??  How did you do this?  Coils produce a spark, they do not get a spark. 

    Charge the battery.  Check if you put the correct plugs.  Get a spark tester and check for spark on 2 and 4.  Check if the injectors are firing on 2 and 4.  Check for injector pulse on 2 and 4 using a noid light.  You can swap coils and injectors to see if the misfire moves.  Check compression on 2 and 4.  Check fuel pressure using a fuel pressure gauge.  Check for a vacuum leak using a smoke machine.  If the valve lash have not been checked in a long time, it might be a cause of the misfire. Good luck.

    • Commenter avatarLog in to reply to the answers
Still have questions? Get answers by asking now.