gas mileage with the 4.5L
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Cadillac Allante Forum Discussion, gas mileage with the 4.5L in Past Cadillac Vehicle Discussion; I have a '91 with the 4.5L and a '93 Eldo with the 4.9L. The Eldo gets 27MPG at cruise ...
  1. #1
    electricman is offline Cadillac Owners Member
    Automobile(s): 93, 98 eldo, 91 allante, '67 GTO
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    gas mileage with the 4.5L

    I have a '91 with the 4.5L and a '93 Eldo with the 4.9L. The Eldo gets 27MPG at cruise while the Allante and the 4.5 gets less mileage.

    Here's the question: why the difference? The cam specs are the same, both use an OD trans, engines are similar xcept for the induction system, my Eldo uses sequential injection with a throttle body, speed/density system, whereas the Allante uses the mass-airflow system, I believe. Perhaps there may be a simple way to improve mileage on the 4.5? It CAN be done as evidenced with the 4.9.

    Anyone ever look into it?

    george

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  3. #2
    RobertISaar is offline Cadillac Owners Member
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    Re: gas mileage with the 4.5L

    i see no MAF in the PCM diagram for a 91 Allante...

  4. #3
    electricman is offline Cadillac Owners Member
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    Re: gas mileage with the 4.5L

    I'll check my manuals tonite; the physical layout seems like it would be a MAF system.

    In any case, what other reasons could there be for the difference in mileage?

    George

  5. #4
    carnut is online now Cadillac Owners Master
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    Re: gas mileage with the 4.5L

    Both are speed density. My first question is what mileage does the Allante get? Also the Allante final drive ratio is numerically higher. Whats the static timing? calls for 10 degrees, but they get better mileage at 12 degrees BTDC. Is the area in front of the throttle body butterflies perfectly clean? Whats the state of tune on the Allante? plugs, fuel filter cap/ rotor.

  6. #5
    RobertISaar is offline Cadillac Owners Member
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    Re: gas mileage with the 4.5L

    i show a 93 4.9 eldorado as having a 2.97:1 FDR...
    i show a 91 4.5 allante as having a 3.21:1 FDR...

  7. #6
    carnut is online now Cadillac Owners Master
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    Re: gas mileage with the 4.5L

    Dare you go!! The Allante is running at a higher RPM at the same road speed as the 4.9.

  8. #7
    electricman is offline Cadillac Owners Member
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    Re: gas mileage with the 4.5L

    Thanx guys.....My service manual and owners manual differ on the FDR on the Eldo, but a difference in the FDR would certainly account for the MPG difference.

    George

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