Deville 04 No code misfire
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Deville 04 No code misfire in Past Cadillac Vehicle Discussion; I have a 04 DeVille with 87k miles, The car was misfiring but after I changed the 2 bad coils ...
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    Deville 04 No code misfire

    I have a 04 DeVille with 87k miles, The car was misfiring but after I changed the 2 bad coils It work good for three weeks only, Now the car back to miss and I replaced all 8 coils with a new set from AC delco ...
    and now the car still miss but less than before,,,

    Symptoms are misfire not that severe when idle only when AC is ON and also become stronger while the car in gear and my foot over brake ....
    Also it jerking and clunking during acceleration from a stop point , all of this happened when AC is ON ...

    The voltage monitor on DIC shows when many loads are present
    like AC is ON and the car in gear with my foot in brake , shows unstable voltage drops to 12.6 and stay until I move the car it back to 14.2 V .

    if AC is Off the miss is hard to notice and there is no clunking and jerking during acceleration ...

    No codes related to PCM , the SES light is OFF . I can provide a video showing the fluctuating voltage under the misfire ...
    Spark Plugs and the fuel filter complete one year now , All 8 coils are changed one bank before may be one month and the other bank is replaced last week ...

    Thanks in advance ...

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    Re: Deville 04 No code misfire

    Try cleaning the TB. Sounds strange, but it has been known to cause a rough idle.

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    Re: Deville 04 No code misfire

    Thanks for info I will clean the TB, I wish it helps and end this time, money consuming proplem...
    Can I use the regular AC Delco carbo cleaner for cleaning the TB ?


    Thanks for your reply...

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    Re: Deville 04 No code misfire

    I don't see why not. I used Gumout carb cleaner til I ran out of it. They do sell a TB cleaner if you'd rather use that. Pretty much anything that will cut the carbon will do. No scraping with steel objects though.

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    Re: Deville 04 No code misfire

    I will go to the end point directly. Today I will scan the car with advanced scanner to figure out which cylinder is mising, and I will buy the carb cleaner..
    Then compare results before and after using the carbo cleaner with the advanced scanner.....

    Any other idea ,,.,.,.

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    Re: Deville 04 No code misfire

    Make sure your cleaner is O2 sensor safe or you will be in for a real learning experience when you have to replace them

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    Re: Deville 04 No code misfire

    Now I finished cleaning the TB,,, It was near clean... Here a picture after cleaning it ...



    In fact the situation is the same, except if I rev up the engine and let the gas the tachometer go to 525 than back to 675 ...
    And I tried to disconnect the MAF sensor to see if the situation changed and no luck !!

    When I turn ON all loads : Lights and AC and put the car in D while foot on brake the voltage monitor show a steady 12.6V ...

    I found something about plenum ( I replaced it recently ) The clamp screw is not tight , I tighten it but nothing enhanced ...

    and about the FPR vaccum line ,, when I disconnect the line from the FPR side, the air is sucked into TB side ...
    So that is it,,, any idea ?

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    Re: Deville 04 No code misfire

    Last night when I went to the shop for scanning, they said for me the scanner will not discover anything unless there is P0300 code current or history !!!!

    And the miss not show up until the car is fully warmed and move a few short miles ( of course with AC on ) ...

    And again there is no misfire during all load changing while AC is OFF !!!!


    So what is the next step ?
    FPR is not leaking there is no raw fuel going out while idling engine and the line disconnected ...

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    Re: Deville 04 No code misfire

    ALL TBs look like the picture above. The fresh air side of the throttle plate never gets dirty. What gets carboned up is the manifold side of the throttle plate. Did you clean that?

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    Re: Deville 04 No code misfire

    sorry but I am not sure that I know about what you mean by the other side Plate ....

    I understand that the other side of the plate is what you see when you push the throttle to the end ...
    If that what you mean, yeas I clean it .....Thanks ....

    I said in post#8 : {{{ And the miss not show up until the car is fully warmed and move a few short miles ( of course with AC on ) ... }}}
    In fact the car also miss after I turn AC on directly,,, wether it warm or not !

    Any Idea ?

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    Re: Deville 04 No code misfire

    Yes, that's what I meant.

    Check the PCV dirty air line where it connects to the rear cam cover and make sure it is tight and there is no vacuum leak there.

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    Re: Deville 04 No code misfire

    [QUOTE=Ranger;3068297]Yes, that's what I meant.

    When the shop replaced the plenum before 2 months they said there is a line -going as I think out of the manifold to the rear cam cover- is leaking ....
    and they said that they fix it .....
    I see that they only covered it with bigger tube without done any replacement ....

    I will check the hoses tommorow, does they produce sound when they leaking ?

    too much "they" !
    Thanks for your advice ....

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    Re: Deville 04 No code misfire

    Depending on how bad the vacuum leak is, it may or may not make a noise. You will definitely hear it with a stethoscope or you can spray any volatile spray like Brakleen around it and listen for an RPM increase.

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    Re: Deville 04 No code misfire

    Good, last time when the car had that severe misfire, I used the stethoscope to check fuel injectors and it was helpfull.....
    I'll see it tommorow , thanks again

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    Re: Deville 04 No code misfire

    Check ALL the vacuum hose connections while you're at it.

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