Deville runs rough under 11 gallons of gas
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HT4100 4.1, 4.5, 4.9 Discussion, Deville runs rough under 11 gallons of gas in Cadillac Engine Technical Discussion; What else do I need to say other than my 93 deville runs rough under 11 gallons of gas. It ...
  1. #1
    joecpwr is offline Cadillac Owners Member
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    Deville runs rough under 11 gallons of gas

    What else do I need to say other than my 93 deville runs rough under 11 gallons of gas. It has done this ever since I bought it 6 months ago at 84,000 miles. I now have 102,000 miles on it. Needless to say I bought it because I spend alot of time driving. I thought I could live with until my last trip...way too many stops to fill up.
    I've tried "Heet" and other additives thinking that there was moisture in the line somewhere but nothing has effected my problem.
    Whenever I have enough gas she runs AWESOME....
    Anyone ever experience this on a Caddy or other GM?
    Thanks -
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  3. #2
    JJhomer83's Avatar
    JJhomer83 is offline Cadillac Owners Connoisseur
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    Re: Deville runs rough under 11 gallons of gas

    Quote Originally Posted by joecpwr
    What else do I need to say other than my 93 deville runs rough under 11 gallons of gas. It has done this ever since I bought it 6 months ago at 84,000 miles. I now have 102,000 miles on it. Needless to say I bought it because I spend alot of time driving. I thought I could live with until my last trip...way too many stops to fill up.
    I've tried "Heet" and other additives thinking that there was moisture in the line somewhere but nothing has effected my problem.
    Whenever I have enough gas she runs AWESOME....
    Anyone ever experience this on a Caddy or other GM?
    Thanks -
    The only thing that is coming up in my mind is the octane your using might effect it

  4. #3
    brougham is offline Cadillac Owners Master
    Automobile(s): 1991 Cadillac Brougham D'Elegance 5.7 Litre
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    My guess is that maybe there's something wrong with pickup or the pump that's in the tank.

    A friend of mine had a Sedan DeVille and a Fleetwood like that and he had some problems sort of like that too. I forget if it was just one of the cars or both that did it.

  5. #4
    joecpwr is offline Cadillac Owners Member
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    JJhomer83 - Octane

    I don't think th octane is an issue - it runs fabulous, flawless, it purrs like kitten and screams like an ape until I get down to about 11 gallons. After that it is no good.

    I'm thinking 'bad' gas would effect it all the time.

    I will add this, the less fuel there is the worse it gets.

    At about 5 gallons it has trouble starting and at less than the motor has died at stop lights.

    Brougham mentioned the fuel pump or pickup in the tank. I have been thinking that also, I just have no experience with this problem nor do I have any experience with gas tanks and fuel pumps.

  6. #5
    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: JJhomer83 - Octane

    The tank issue is VERY common on these cars.......

    Most of the time it happens when the tank is below half and especially bad when going on turns.......

    There is a restyled tank that prevents this.....

    My advice would be to replace the tank, the pump, and the fuel filter....... That should take care of it.!!!!!!

  7. #6
    Shoehorn is offline Cadillac Owners Member
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    Also, the modern electric fuel pumps that are in the tank actually use the gas in the tank to dissipate heat. Perhaps the pump is overheating after the fuel level drops to a point where it is no longer submerged.

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