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Thread: 1994 Deville Concours Misfire Diagnosis

  1. #1
    IvanDeVille is offline Cadillac Owners Member
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    1994 Deville Concours Misfire Diagnosis

    I have a 94 Concours that's misfiring and I can't figure out what's causing it.

    So far I've replaced the spark plugs and cleaned around the air flow sensor and that hasn't done it.

    Any recommendations on what I can try next?

    P.S. when I replaced the plugs it was running smoothly for about 2 days, and then the knocking/misfire came back. And the knock only happens when the car is idling, it's smooth when the car is moving.


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  3. #2
    amunderdog is offline Cadillac Owners Connoisseur
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    Re: 1994 Deville Concours Misfire Diagnosis

    Is it showing any codes?
    http://www.cadillacforums.com/forums...odes-dtcs.html
    If so please include definitions

  4. #3
    ofnaman is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Make sure the spark plug wires don't have carbon tracking on them. I see this all the time, a customer will have the plugs replaced due to a misfire concern somewhere else or the will do it themselves and didnt change the wires. One of the most common issues I see with misfires on these engines are cracked spark plug porcelins, and that will create carbon tracking on the wires which will come back as a misfire, usually in a week or so. The other issue I see is rusted coil posts on the coil to wire connection. I'm not saying that's what it is, just giving some friendly advice.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    When was the TB last cleaned?

  6. #5
    IvanDeVille is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Quote Originally Posted by amunderdog View Post
    Is it showing any codes?
    http://www.cadillacforums.com/forums...odes-dtcs.html
    If so please include definitions
    I haven't checked, I'll check tomorrow and post what I find.

    ----------

    What exactly is carbon tracking? Do I check for it just on the wire or on the new plug as well?

    ----------

    I cleaned it when I cleaned the air flow sensor, didn't really seem to help.

  7. #6
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Carbon tracking is when the current finds an easier path, down the side of the plug as opposed to through it. On the plug it will sometimes look exactly like the porcelain is cracked. It cannot be cleaned off. The track will also be transferred to the plug boot. It's not real common, but if you find it you MUST change both the plug and boot together.








  8. #7
    IvanDeVille is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Alright cool, I'm going to try to find it right now will be back with what I see.

  9. #8
    IvanDeVille is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    pulled codes here they are
    *current* S038 - Electronic Level Control Exhaust Valve Short to Ground/Open (Road Sensing Suspension)
    *current* S061 - Right Front Position Sensor Fault (Road Sensing Suspension)
    *history* P028 - Open 3rd or 4th Gear Shift Or Shorted 2-3 Shift Solenoid [VCC] (Engine/Transmission)
    *history* S011 - Left Front Damper Solenoid Valve Short to Ground/Open (Road Sensing Suspension)
    *history* S060 - Left Front Position Sensor Fault (Road Sensing Suspension)

    And I looked for the carbon tracking on the plugs and wires and couldnt see anything.

    ***Looks like the cam cover seals are leaking into the plug holes as well, don't know if this could be causing the problem? See attached pics.

    IMG_00000370.jpgIMG_00000371.jpgIMG_00000372.jpgIMG_00000373.jpg

  10. #9
    IvanDeVille is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    The cam leaks are only on the even plug side (side facing the front of the car)

  11. #10
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    Ranger is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Oil in the plug wells is normal and unrelated.

  12. #11
    Caddy-EaRL's Avatar
    Caddy-EaRL is online now Cadillac Owners Enthusiast
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    Quote Originally Posted by Ranger
    Oil in the plug wells is normal and unrelated.
    Normal? Hmmmz although the small amount on his plugs most likely isn't causing a problem, it's only normal if the tube seals are leaking. I haven't actually seen many caddys with bad tube seal leaks, but I've seen several Nissans, Hondas, and Toyotas that leaked so bad it deteriorated the plug wires and caused awful misses.

  13. #12
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    Maybe I should have said somewhat common? At least that's my interpretation from my own experience and from what I've seen (read) here. I can't say that I've ever seen or heard of them being THAT bad though.

  14. #13
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    I'd say at least half of the members here that remove/replace the plugs, have oil in the if wells.

  15. #14
    IvanDeVille is offline Cadillac Owners Member
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    Re: 1994 Deville Concours Misfire Diagnosis

    What's the next step for the misfire?


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