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2004- OBD Code P0304 where is cylinder #4?

Discussion in '2002 - 2005 Ford Thunderbird' started by 04tbirdjerry, Feb 12, 2019.

  1. According to chart I have, the #4 cylinder is on pass side, nearest to firewall. I checked the harness, replaced both the plug and coil pack, and I still have rough idle and keep pulling code 0304 (misfire cylinder 4) and 0316 (misfire detected first 1000 revolutions). WTF? Is my chart wrong? Is #4 back pass ? Thanks for any suggestions and/or help.
  2. biddle

    biddle Forum Moderator Staff Member

    Please include the model year(s) of the car in the subject of the post on future posts. I've added this for you.
    ChuckH262 likes this.
  3. You have the right location for #4. Can you clear the code, and see if same code comes
    up again.
    biddle likes this.
  4. Thank you, yes, cleared the codes and they came back again. Car idles rough, but has power once moving. Not sure what else it could be. I also put some Seafoam injecter cleaner in last refill, in case that particular injecter was dirty. Plan to repeat that as it is recommended if you've never used before.
  5. biddle

    biddle Forum Moderator Staff Member

    You can also put 2002-2005.
    We have members with 1955-2005 models. Once a week a popular posts email is sent, it makes it easier to determine on the summary what year the post is about. Also, when the post is indexed in Google, it helps with SEO because the model year is in the URL.
  6. biddle

    biddle Forum Moderator Staff Member

    Here is a good thread to read about COPS and Spark plugs- https://forums.fordthunderbirdforum...-05-ford-thunderbird-ignition-coils-cop.5040/
    04tbirdjerry likes this.
  7. This isn't fun to bring this up, but how do you know that the new coil you used to replaced the existing one is truly a good coil? New does not always mean good & usable. I would take that new coil out & swap it to another cylinder. Easy to do since you have the cover off. See if this moves the problem. Truth be told if I went through the effort to remove the cover I would replace all of the coils on that side.
    Pelagic likes this.
  8. I did perform the old school screwdriver test. Coil off plug, but hot. Started motor and inserted driver into coil boot, was able to still get a spark jumping from boot to driver up to 1/2" away. This is best way to know you're getting juice to the plug. I'm perplexed now.
  9. Last edited by a moderator: Feb 13, 2019
    Pelagic and biddle like this.
  10. Pelagic

    Pelagic Well-Known Member Lifetime Donor

  11. Well, bad news, I pulled (and tested first) and replaced all 8 coil packs, and all 8 spark plugs. I tested each new coil to make sure good spark was there. I did each cylinder at a time, and restarted engine each time to see if rough idle/miss fire was present. Idle still rough (different issue probably), but has great power when pulling. Cleared all codes. Pulled 0304 and 0316 again. Cleared again. Check light came on again, tested and pulled same codes again.
    I'm about to give up and take to dealer (and dread that phone call with repair estimate), but first I will address rough idle. Who knows, it may stop those codes from coming back. Cylinder #4 is definitely getting fire, so it must be something else causing those codes to register on my OBD II.
  12. Have you tried disabling all eight coils one at a time, to see which ones
    make car idle different.

    Could your egr valve be stuck open.
  13. When replacing each coil, I ran engine while coil was out, then again while each new coil was out, then again while each new coil was installed. I never noticed any change at low idle (rough on every one), that's why I think it's not cylinder #4.. I did just buy a new part recommended on this forum. I will replace that and report back.
    Thanks so much for your input, I hope that part will let engine breath right.
    I will advise outcome, thanks again.
  14. OMG, after driving car around, choking for two months, I wish I had old schooled the garden hose trick. Turns out that my intake gasket failed right at cylinder #4. There was an air leak right there; tech found a piece of gasket blown out. Kudos to London Bridge Auto for sorting it out. They replaced gasket ($495) and now my Tbird hauls ass again! Shows you you can't manage maintenance by OBD codes alone.
    stevedaphotoman, Mach5 and BluByeU like this.

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