1978 Seville runs crappy with misfires and rough idle
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1978 Seville runs crappy with misfires and rough idle in Past Cadillac Vehicle Discussion; Hello my friends My Cadillac Seville's starter broke down 1 week ago (Seville 1978 350 cui petrol), I replaced it ...
  1. #1
    ploppysator is offline Cadillac Owners Member
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    1978 Seville runs crappy with misfires and rough idle

    Hello my friends

    My Cadillac Seville's starter broke down 1 week ago (Seville 1978 350 cui petrol), I replaced it with an used one. After this, the car was running perfectly again, except, that the V-belt to the alternator was squieking, caused by an incorrect tension.

    I was driving on the motorway two nights before and it was freezing cold and snowing like it was always during this entire winter.

    suddenly I saw the lights going darker and stopped at a parking space. after this, the car didn't start anymore, the battery was completely discharged. replacing the tensionning screw on the alternator and boosting the car for starting helped and the alternator was delivering enough power, all was running ok afterwards until yesterday morning.

    I intended to drive to a destination about 100 miles away and from beginning, the car run rough, had a rough idle speed and had misfires all the time, specially, when I lifted the foot from the gas. Additionally it was blowin unburnt petrol through the exhaust pipe.

    where can this be coming from, I gave it more oxigen by turning the air screw on the carburetor, but it is still the same. Additionally I have to mention, that when I press the gas hard, black smoke comes out of the exhaust pipe and the car used too much petrol also.

    can anybody please help?

    thank U

    Ploppy

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 1978 Cadillac Seville runs crappy with misfires and rough idle

    You might want to look through the Engines forum threads for tips on this particular engine and its maintenance.

    Europe ??? Switzerland ??? If you're outside the U.S., you might want to update your profilke to reflect location - it sure helps when we need to find parts and such.

    Welcome Aboard !!!

  4. #3
    Ranger's Avatar
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    Re: 1978 Cadillac Seville runs crappy with misfires and rough idle

    Sounds like an ignition problem (unburnt fuel out the tile pipe). You might try charging the battery. It's possible that the alternator could not charge the battery from a dead state (which is not a good idea in the first place) AND keep up with the load.

  5. #4
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Cadillac Seville runs crappy with misfires and rough idle

    I replaced the battery, but it's not getting better.

    Additionally I found out, that there is a vacuum sound and the brakes are not working properly anymore. Does anybody have a vacuum diagram for this car?

    thank U

    regards

    Bruno

  6. #5
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    Re: 1978 Seville runs crappy with misfires and rough idle

    No diagram, but the HVAC and parking brake release are vacuum operated (all under the dash). Parking brake release diaphragm is a common leak point, but as old as it is, all vacuum lines are possibilities.

  7. #6
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Today i checked the spark plugs, two of them where wet with petrol and all where black, so I cleaned them and gave more air, but it wasn't better afterwards.
    Thenk I removed the distributor cap and removed all traces of oxidation on all contacts and the rotor and placed it back, where it was.

    Now, the car doesn't start anymore at all .

    As the rotor was not turned and all wires where placed back, where they belong to, I am confused about what could have happened.
    Does anybody have an idea, what I should and can do next?

    thx

    Bruno

  8. #7
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Over time the cap contacts erode from the spark. Cleaning it may have enlarged the gap to more than the spark can jump. Maybe it's time for a new cap & rotor.

  9. #8
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    do you know if it is possible to take the cap and rotor from my 76 Chevy Caprice and use it in my Seville?

  10. #9
    rodnok01's Avatar
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    Yes. Gm hei distrib caps & rotors all the same IIRc

  11. #10
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    thank U

  12. #11
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Today I replaced the distributor cap, the rotor, the coild, the sparks and all wires with new ones, but the problem is still the same, except that the sparks are only sooty and not wet anymore. when I start the engine it runs but as soon as I change to R or D, it switches off, if I don't press the gas down and the misfires are still there. As far as I can see from a visual check, the fuel pressure is oK (about the same as it alwys was).

    as the problem is still on the same 2 cylindres as before, can it be related e.g. to the injectors or even the ECU?

    how do I check the injectors without removing them?
    how do I check if the car has a problem with the electric ground?

    has anybody another idea about what to check?

  13. #12
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Quote Originally Posted by ploppysator View Post
    how do I check the injectors without removing them?
    Listen to each one with a stethoscope (or screwdriver). Each one should have the same rhythmic ticking.

    how do I check if the car has a problem with the electric ground?
    Run a redundant ground from the negative battery terminal to a good ground using a wire with alligator clips (even a jumper cable will do).

  14. #13
    rodnok01's Avatar
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    He has a carb... at least he said he adjusted the carb in 1st post.
    Sounds to me like the vacuum advance is messing up or your timing is off since it is onlt doing it in gear.

  15. #14
    Ranger's Avatar
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    Re: 1978 Seville runs crappy with misfires and rough idle

    That's what I thought, but he said "how do I check the injectors without removing them?". I assumed he knew what he had.

  16. #15
    rodnok01's Avatar
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    I'm not sure he does either. Think a lot is being lost in translation
    Could very well be the carb

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