Help with 2005 STS misfire P0304
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Cadillac STS Forum - 2005 through 2012 Discussion, Help with 2005 STS misfire P0304 in Past Cadillac Vehicle Discussion; I've got a reading on my CarMD of P0304, cylinder 4 misfire. I've searched through this forum and it appears ...
  1. #1
    CTS11723 is offline Cadillac Owners Member
    Automobile(s): 2005 STS
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    Help with 2005 STS misfire P0304

    I've got a reading on my CarMD of P0304, cylinder 4 misfire. I've searched through this forum and it appears the consensus is that the plugs should not go bad before 100,000 miles. I've got 76,000. I am assuming that the coil pack that connects to the plug may have a bad connection or gone bad.

    Sometimes it is very obvious that there is a misfire. Shaking, bad acceleration. I can hear and feel it. Then other times I'll start it up and it is as smooth as can be. Today while coming home, it started out smooth and then started shaking again.

    I'd like to take off the engine cover so that I can access the plugs and wires. If I read correctly, I just need to remove the caps and yank it off. Also, how do I know which cylinder is which?

    Thanks.

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  3. #2
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
    Automobile(s): 2006 STS4 V8 1SG & 2007 STS V8 1SE
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    Re: Help with 2005 STS misfire P0304

    Does it vary with damp weather? Is there any pattern?

    A set of OEM plugs wouldn't be a waste of money if you're planning to keep the car.

  4. #3
    Pjazz's Avatar
    Pjazz is offline Cadillac Owners Fanatic
    Automobile(s): 2007 STS 1SG V8 RWD
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    Re: Help with 2005 STS misfire P0304

    Quote Originally Posted by EChas3 View Post
    Does it vary with damp weather? Is there any pattern?

    A set of OEM plugs wouldn't be a waste of money if you're planning to keep the car.
    Ditto

  5. #4
    CTS11723 is offline Cadillac Owners Member
    Automobile(s): 2005 STS
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    Re: Help with 2005 STS misfire P0304

    I think it does vary with the damp weather as I am in the Albany, NY area and we have had a bit of rain this week. It was worse in the morning and then after the engine was heated it would smooth out. The only exception to that theory is today. It was bad in the morning and very damp. The engine smoothed out and was fine when I drove at lunch. After work, it was very humid and started smooth then started shaking a few miles out.

  6. #5
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
    Automobile(s): 2006 STS4 V8 1SG & 2007 STS V8 1SE
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    Re: Help with 2005 STS misfire P0304

    Classic failing coil symptoms lead me to suggest you check with Chris at Rippy's for a coil. Keep track as others go.\

    Consider stepping up to a garage. Exposing a valuable asset to the elements will increase maintenance requirements.

  7. #6
    CTS11723 is offline Cadillac Owners Member
    Automobile(s): 2005 STS
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    Re: Help with 2005 STS misfire P0304

    Update on misfire. I ran the diagnostics again and I've got P0304 and P0204. Someone else in the forum left a link to a site with great information http://www.aa1car.com/library/misfire.htm

    It says that if both of these codes are returned, that I've probably got a bad injector. If it was the coil, the code would have been P0354 Ignition Coil 4 Control Circuit along with the P0304.

    I think I am going to start with finding someone to do an off-car injector cleaning as recommended here: http://www.aa1car.com/library/2003/ic30336.htm

  8. #7
    cdezey is offline Cadillac Owners Member
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    Before u go through that find someone with a pro scantool u will get a lot more info, the codes u have are just that u need voltage- resistance etc etc.

  9. #8
    CTS11723 is offline Cadillac Owners Member
    Automobile(s): 2005 STS
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    Re: Help with 2005 STS misfire P0304

    Here's the latest. Replaced plugs, ignition coil on both #3 and #4 and also injectors for #3 and #4 (All AC Delco OEM). Still getting the same codes. Noid test failed on these 2 connectors on the harness.

    Should I look to replace the harnes or could this be a problem with the ECM?

    Also, does anyone know the part number for the fuel injector wiring harness? I have searched everywhere and can't find it.

  10. #9
    mdmings517 is offline Cadillac Owners Member
    Automobile(s): 2005 STS V6
    Join Date
    May 2011
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    2

    Re: Help with 2005 STS misfire P0304

    What was the finally result of this problem? I am having the same issue. I have replaced coil and plugs all 6.

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