1978 Seville runs crappy with misfires and rough idle - Page 2
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1978 Seville runs crappy with misfires and rough idle in Past Cadillac Vehicle Discussion; A '78 Seville is fuel injected....
  1. #16
    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    A '78 Seville is fuel injected.

  2. #17
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    hi all

    I suspect the injectors, as only on 2 cylindres the sparks were very black and drawning in petrol. if there is a problem with the carburetor, it would be on all eight wouldn't it?

  3. #18
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Now I am totally confused. Is it carbureted or fuel injected?

    If it is injected, you may have two leaky or stuck open injectors.

  4. #19
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Yes to both Ranger... think those years had the EFI with injectors, but uses the "throttle body" carb setup, cannot remember the name for that setup. There are some adjustments you can make to the "carb".
    They are very picking to work on from what I remember.
    So he probably does have bad injectors.

  5. #20
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Quote Originally Posted by rodnok01 View Post
    Yes to both Ranger... think those years had the EFI with injectors, but uses the "throttle body" carb setup, cannot remember the name for that setup. There are some adjustments you can make to the "carb".
    They are very picking to work on from what I remember.
    So he probably does have bad injectors.
    Correct, though I'm no expert I had a 1978 Seville Elegance with 350 Olds "fuel injected" engine. It did indeed have a throttle body carb setup on top of the motor but also a set of injectors, wish I could recall what GM named it, but it escapes me at the moment. Mine eventually started surging at idle but I never had the problems ploppy is having, for me it was a new set of injectors and some vacuum leak repair. This was over fifteen years ago mind so I don't recall the specifics.

  6. #21
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Are you guys talking about the "throttle body injection" with 2 injectors in the TB?

  7. #22
    cadillac kevin's Avatar
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    Quote Originally Posted by Ranger
    Are you guys talking about the "throttle body injection" with 2 injectors in the TB?
    the olds 350 in the seville had injectors mounted in the intake runners near the heads (port injection?).

  8. #23
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    exactly, the Chevrolet engines (eg. the 76 Caprice) have throttle based injectors, but the Olds 350 used in the Sevilles have a fuel rail over the intake manifold with injectors on top of each cylindre (Bendix system). As I suspect the injectors to be broken, I replaced today the whole intake manifold, the entire fuel rail, the carburetor and all injectors, but as 2 of them are leaking I have to fix this, before I can try (actually there is no pressure in the fuel rail), will keep you informed about tomorrow

  9. #24
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    hello all

    the leak is fixed.

    I have a good battery, fuel on the fuel rail and enough pressure, the fuel pump is working, so there is enough air and enough fuel, but the car doesn't start at all,
    As I replaced the sparks, the spark wires, the distributor and rotor, I have no idea, why the car does not start, but I had a similar symptom already once, when the connection to a sensor, located on the driver's side cylindre head, between the 2 rear sparks (1 wire, the sensor is mounted on an about 8 inch long screw), broke off. Can this be related to this sensor, as I only grounded the wire the last time and it is still only grounded?

    I didn't find out, what this sensor is used for...

    any other good idea? thank you in advance

    Bruno

  10. #25
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    Re: 1978 Seville runs crappy with misfires and rough idle

    That sensor won't keep the car from running. I would check the distributor wiring and internals. GM are notorious for chaffed wiring and the module going out. You did put the button back under the coil in distrib cap correct?

  11. #26
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    Quote Originally Posted by rodnok01 View Post
    TYou did put the button back under the coil in distrib cap correct?
    hi

    first I didn't put it correctly back, but then I checked with the old one and fixed it but the result was the same: not running. I will check the wiring and the spark again and will post what happened afterwards. Even if the sensor is not the cause, do you know, what it is for?

    thank U

  12. #27
    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 again: there is, but it is rather orange, than blue, looks very weak.

    I checked the ground, it is good at the frame and the engine. At the pink wire and at the distributor/coil i have - as long as the ignition key is at the off position - somewhat over 13 Volts, but as soon as I turn the key, it falls down to 0.120 and goes up to 0.600 Volts as soon as the starter turns.

    Could a broken ignition key lock cause all before mentioned and also this problem?

    thank U for all answers

  13. #28
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    hi all

    could a damage in the distributor itself cause only orange spark lights?

  14. #29
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    Probably not. Weak coil more likely than that

  15. #30
    ploppysator is offline Cadillac Owners Member
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    Re: 1978 Seville runs crappy with misfires and rough idle

    *** PROBLEM SOLVED ***


    dear friends

    thank you for all your help and instructions .

    my poor car suffered from multiple problems :

    - the ignition module (I tried out three of them) were faulty, bought another new one, additionally the pickup coil was burnt and and the magnet on top was broken, so they had to be replaced, too

    - at last, the garage, that installed the starter motor constructed a short-circuit by letting the + cable from the battery to touch the exhaust pipe when driving, problem didn't occure while standing

    so finally, the car got back on the road again, I still have to fine-tune the distribution, this was the first time I was setting this up by miself without an diagnostig light, but at least it is running again.

    thank you for all very, very appreciated help from all, I learnt a lot during the recent few weeks.

    good times and rides for all

    Ploppy

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