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Gas mileage drop WOW

Discussion in 'Off Topic Threads' started by ntgr8, Jan 2, 2013.

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  1. ntgr8

    ntgr8 Member

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    Mileage went from 23mpg to 9mpg in one tank of gas, any ideas as to why? 98 cadillac deville concours 125k miles. Seems you guys know everything maybe get an idea before going for service. By the way the car runs fine.
     
  2. davidjayuden

    davidjayuden Well-Known Member

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    Wow! A teenage son with a siphon hose?
    dju
     
  3. mixer

    mixer Well-Known Member

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    Did you get that number by actual mileage driven and amount of fuel at refill or by looking at fuel gauge? You could have a bad fuel gauge sender in the tank.

    Fill up the tank until the auto shut off stops the pump. Drive 200 miles and refuel until auto shut off stops the pump. See how much fuel it takes and do the math.

    Eric
     
  4. oldgahchamp

    oldgahchamp Active Member

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    I would check for a leaky gas line first. Larry
     
  5. OldRemFan

    OldRemFan Member

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    I don't know how much your caddy tank holds, but if it is less than 20 gallons you may not want to drive 200 miles before refueling if you are actually only getting 9 miles per gallon. The last few cars I have owned don't have that large a gas tank.
     
  6. 548

    548 Guest

    02 sensors are killer on mileage, but your check engine light would be on if the 02 sensors were shot.
     
  7. Barrelbulge(Fl)

    Barrelbulge(Fl) Banned User Banned TS Supporters

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    Is your catalytic converter shot?
     
  8. Shootrman

    Shootrman Member

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    Possibilities
    Fuel leak
    Oxygen sender
    Fuel sending unit
    Odometer going bad/ just shows bad mileage
    Or, hate to say this, we're all getting older, did you write down the right numbers on your last fill-up or maybe the wrong number this time, giggle
     
  9. ntgr8

    ntgr8 Member

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    mpg info from onboard computer, tells range, avg mpg, instant mpg, avg mph etc.
     
  10. blizzard

    blizzard Active Member

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    Subject: Gas mileage drop WOW
    From: 548
    Email:
    Date: Wed, Jan 02, 2013 - 11:38 AM ET
    Website Address:

    02 sensors are killer on mileage, but your check engine light would be on if the 02 sensors were shot. - 548


    Why even post that if you know you're providing 0 help????
     
  11. HSLDS

    HSLDS Well-Known Member

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    Blocked Cat Converter.

    Bad O2 sensor

    Emergency brake stuck on
     
  12. oz

    oz Active Member

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    Were you pulling your 30' motor home?
     
  13. LUGNUTZ426

    LUGNUTZ426 TS Member

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    above and beyond what was already stated about clogged exhaust and bad o2 sensors. retarded valve timing, clogged air filter/intake, fuel pressure too high. bad maf sensor. should be mil codes stored pointing to issue. have someone put a scan tool on it.
     
  14. blizzard

    blizzard Active Member

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    Subject: Gas mileage drop WOW
    From: 548
    Email:
    Date: Wed, Jan 02, 2013 - 01:54 PM ET
    Website Address:



    548aturd- You still didn't answer my question.
     
  15. Johnny

    Johnny Well-Known Member

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    A car that went from 23mpg to 9mpg would not likely "runs fine" and there should be obvious problems. Double check the computer
     
  16. Dr.Longshot

    Dr.Longshot Banned Banned

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    How cold is it where you live? My gas mileage really went down when it went to 4 degrees,This normal when the computer is setting air/fuel ratio vs air temp


    Gary Bryant
     
  17. stokinpls

    stokinpls Well-Known Member

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    Guess you could always try unhooking the battery for a couple hours. Maybe the computer's confused (if it has one). Wouldn't cost you much.

    Maybe it's actually getting 19 mpg and the "1" is burned out? ;-)

    Bob Falfa
     
  18. StonewallRacing

    StonewallRacing Well-Known Member

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    Did your wife put E85 in it?

    SW
     
  19. ntgr8

    ntgr8 Member

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    Cold as hell but that never mattered much, some drop in mpg but not alot. No E85, wife never and I mean never put gas in the car. Will have answer tomorrow at 9 am.
     
  20. Ross

    Ross Well-Known Member

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    Will be interested in your findings, sounds like a leak, hope it's something simple. Ross Puls
     
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