My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help.
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Cadillac Seville / Cadillac Eldorado Forum Discussion, My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help. in Past Cadillac Vehicle Discussion; First off I would like to say thank you for all the help in the past. Never joined just lurked ...
  1. #1
    Alex 92 is offline Cadillac Owners Member
    Automobile(s): 1992 Cadillac 390HP 4.9 Eldo and many many more
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    My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help.

    First off I would like to say thank you for all the help in the past. Never joined just lurked around researching.

    My 92 4.9 ESC Is my baby. She was bought new in 92 and has 71000 original miles on her.

    All service myself and done on time everytime. All GM/Delco parts.

    No codes... Current or history...


    I recently ran 3k PM's on her. Oil was changed. PF61 Delco primed and 5 qt.s of Mobile1 Gold synth.

    After 3 days about 160 miles when motor warmed, it would have a rhythmic idle.like a shudder in sync with the compression burst. When I would reverse with light gas it would jerk in sync with the rpm. It's like a vibration. Shift to drive and pull away and it would do the same the in sync with rpm.

    Seemed to smooth out until overdrive where it would do it again due to rpm drop.
    At stop it would idle real ruff and when I pull off the car would jerk in rythum with the motor.

    It does this in reverse,forward,drive and in park. It idles ruff warm and just a slight raised throttle it shutters about 1500 rpm and again at 4500 rpm. It does it all the time during acceleration just not as bad.

    Mounts good. New plugs etc. Electrical PM Done. No codes. Trans PM Done. Emissions good. Pressures all good.

    Help!!!!!!

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    delerium75's Avatar
    delerium75 is online now Cadillac Owners Fanatic
    Automobile(s): 1991 STS, 1992 Fleetwood, 1987 Maxima wagon
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    Re: My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help.

    Fuel injectors all ok?

  4. #3
    Alex 92 is offline Cadillac Owners Member
    Automobile(s): 1992 Cadillac 390HP 4.9 Eldo and many many more
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    Re: My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help.

    Yes.. I checked them out.. This happens after the motor is hot.. You can hear it the exhaust as well.. ???

  5. #4
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
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    Re: My 92 4.9 ESC.. Rythmic motor shudder..? Loss of power..Please help.

    It definitely sounds like a misfiring cylinder. Ignition or fuel is most likely the problem.

    Isolate the cylinder by pulling individual plug wires until you find one that makes no change in the way the engine runs. When firing cylinders are disabled, RPM's will drop slightly and the engine will run rougher. When misfiring cylinders are disabled, no change will occur.

    When you find the problem cylinder, verify properly working ignition to that cylinder. If you find a problem, repair it. If everything checks out, move on to fuel.

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