79 eldo wont run when warm
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5.0 and 5.7 Discussion, 79 eldo wont run when warm in Cadillac Engine Technical Discussion; Recently bought a 1979 Eldorado. Only paid a couple of grand for it but its all there. Just needs some ...
  1. #1
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    79 eldo wont run when warm

    Recently bought a 1979 Eldorado. Only paid a couple of grand for it but its all there. Just needs some paint and some fillers. 105K on the motor which runs great until it warms up. It starts right up and drives like a champ...then it warms up and it runs like ass. Wont take the fuel I'm thinking. Hesitation, intermittent
    surging. I replaced the EFI air and coolant sensors with no change. Any ideas? Computer maybe? I know a lot of people just get rid of the EFI and go with a carb setup but I would rather leave it stock. Thanks\

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    carnut is offline Cadillac Owners Master
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    Re: 79 eldo wont run when warm

    The MAP sensor is built into the ECU. When started cold, the computer works off a pre determined fuel curve, once warm it gets info from sensors. I think the MAP sensor could be the culprit.

  4. #3
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    Re: 79 eldo wont run when warm

    thanks man...kinda figured that's what was up. Just wanted to make sure I wasn't missing something else. Got reman ECU on the way!

  5. #4
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    Re: 79 eldo wont run when warm

    ok so swapped out the ECU. replaced MAP hose and other vacuum lines while I was at it. NO Change. If I feather the accelerator ever so slightly I can get it up to speed...barely. But if I try to give it the gas it will bog. Doesn't stall. Idles fine. I was thinking Fuel pressure or a clogged filter but it runs fine when cold. you can give it as much as you want. Just when it warms up. Warmer it gets worse it runs. Any other suggestions would be greatly appreciated Thanks

  6. #5
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    Re: 79 eldo wont run when warm

    changed fuel filter no change

  7. #6
    fixitman's Avatar
    fixitman is online now Cadillac Owners Member
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    Re: 79 eldo wont run when warm

    try checking your fuel pressure, you could have a bad pump.

  8. #7
    Zachary Smith is offline Cadillac Owners Member
    Automobile(s): 1979 Eldorado
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    Re: 79 eldo wont run when warm

    Perhaps we could make a partial swap. Mine doesn't want to run when cold.

  9. #8
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    Replaced fuel pump no change...running out of things to change. Should just change the damn thing over to carb and call it a day. But now I want to just fix it out of spite

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 79 eldo wont run when warm

    tinnokkr .............. ex-Ship's Serviceman or Machinist ?

  11. #10
    tinnokkr1 is offline Cadillac Owners Member
    Automobile(s): 1972 Eldo Conv, '88 D'Elegance,06 Escalade ESV,79 Biarritz
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    Neither...just a sheet metal mechanic.Have a shop up here in MA. .HVAC

  12. #11
    Zachary Smith is offline Cadillac Owners Member
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    Re: 79 eldo wont run when warm

    This is quite likely the manifold temperature sensor. It doesn't effect much until after the coolant sensor has detected a warm engine. I am too cheap/ couldn't find
    replacements for both sensors. There are many sensors available for "Intake air charge temperature". Do not buy. They are all wrong. They have the newer Negative
    temperature coefficient response. The Haynes manual is wrong. The resistance should rise with temperature, not lower. I have installed "guitar pots" temporarily to test.
    I can know customize my EFI to fool it into whatever mixture I want. I am sure any potentiometers that you can control between 400 - 4000 ohms would work great.

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