4.9L missing
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9L missing in Cadillac Engine Technical Discussion; So the motor hesitates on excelleration. Gas mileage is kinda crappy. Motor runs 'okay' but really feels like at least ...
  1. #1
    primerib is offline Cadillac Owners Member
    Automobile(s): 95 Deville
    Join Date
    Aug 2009
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    56

    4.9L missing

    So the motor hesitates on excelleration. Gas mileage is kinda crappy. Motor runs 'okay' but really feels like at least 1 cylinder is misfiring.

    So I need to find the misfire. Any recommendations where to start? I've never had to find a cylinder misfire before.

    Thanks in advance.
    D

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  3. #2
    daniel58 is offline Cadillac Owners Fanatic
    Automobile(s): 58 Coupe Deville, 77 Coupe deville, 90 Deville
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    Re: 4.9L missing

    I have a 90 4.5 with similar problems. There are so many things to check it would be hard to list them all here. You could start with and inspection of the vacuum lines and then cap, wires and plugs, fuel pressure, use noid lights to check that the injectors are getting a signal. Compression check also. I have done all of this stuff to my 4.5 and it still misses!!! Good luck with GMs finest, those plugs are a real bear to change. I know because I have changed mine 3times in the last month, if I had a Cadillac engineer handy this afternoon I would have beat him to death with a crowbar! Or worse yet made him change those plugs.

  4. #3
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): 2011 Crown Vic LX
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    Re: 4.9L missing

    There's always worse, man. Ever try doing ANY type of repair on a Ford 2.5L Duratec? You have to take the intake manifold off to do pretty much anything...

    Even better, the Mazda trans that's usually bolted to it isn't serviceable.

    Hang in there, you'll get it.

  5. #4
    primerib is offline Cadillac Owners Member
    Automobile(s): 95 Deville
    Join Date
    Aug 2009
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    56

    Re: 4.9L missing

    thanks daniel. I was thinking injectors and compression for low hanging fruit. I've recently changed the plugs/wires/distributor cap/rotor button and those didn't help.

  6. #5
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): 2011 Crown Vic LX
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    5,320

    Re: 4.9L missing

    Well, if you think you have a 1 cylinder misfire, first step is to isolate the cylinder.

    The easiest way is to use the onboard diagnostics to do the cylinder balance test. Do you know how?

    Otherwise, use the classic method. Engine off, open the hood and pull a spark plug wire from the distributor cap. Set the wire back on the cap terminal put don't seat it all the way. Just let it set on the terminal so it will be easy to pull off again. Do so for the other 7 wires.

    Fire up the engine and start pulling those plug wires, one by one, listening for a change in how the engine runs. The one that makes the least or no difference is the affected cylinder.

    After isolating the cylinder using either method, go on by checking for spark, fuel, and compression on that cylinder.

  7. #6
    quins90lac's Avatar
    quins90lac is offline Cadillac Owners Enthusiast
    Automobile(s): 1990 Cadillac sedan devile
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    Peoria IL USA
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    Re: 4.9L missing

    Quote Originally Posted by drewsdeville View Post
    There's always worse, man. Ever try doing ANY type of repair on a Ford 2.5L Duratec? You have to take the intake manifold off to do pretty much anything...

    Even better, the Mazda trans that's usually bolted to it isn't serviceable.

    Hang in there, you'll get it.
    you don't mean the M5OD would ya

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