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  1. #1
    19Cutlass94's Avatar
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    Why is my car using so much gas?

    Recently I drove like 390 all highway miles, and i only got 25mpg... on straight highway! I mean maybe it was because it was going like 70-75 some of the time, but that cant be the whole reason as to why. Is it possible I might have an injector thats stuck open or leaking? Would i be able to test this by ohm testing the injectros or no?
    Jay

    1994 Oldsmobile Cultass Supreme SL
    3400/Getrag 284 5spd
    1995 Chevy K1500 350c.i. 5spd Z71
    350/NV3500 5spd
    2014 Chevrolet Malibu LS
    Stock - Daily Driver

  2. #2
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    Re: Why is my car using so much gas?

    you ought to see why my Intyrigue is getting and you would stop bitching about it ~

  3. #3

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    Re: Why is my car using so much gas?

    Quote Originally Posted by All Your Intrigue Are Belong To Me
    you ought to see why my Intyrigue is getting and you would stop bitching about it ~
    But you don't count. You only operate the car at 100% open throttle and over 100mph as much as possible.


    BUILDER AND DESTROYER OF FINE(?) AMERICAN CARS.

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    Lurker Captain Ficho's Avatar
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    Re: Why is my car using so much gas?

    Change your fuel filter lately?
    DD's:
    1997 Volvo 850 wagon - 265k miles - T5 turbo, 5spd, awd... 1 of 214

    Toys:
    1987 Buick Grand National - 71k miles - Show car/garage queen... 426whp
    1995 Pontiac Grand Prix GTP - 181k miles - built LQ1... turbo 3800 coming soon.

  5. #5
    Addicted to eaton's Avatar
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    Re: Why is my car using so much gas?

    Quote Originally Posted by Crazy K
    Quote Originally Posted by All Your Intrigue Are Belong To Me
    you ought to see why my Intyrigue is getting and you would stop bitching about it ~
    But you don't count. You only operate the car at 100% open throttle and over 100mph as much as possible.
    i get 26 avg in my l67
    2010 Chevy Silverado 325 5.3L Vortec Z71 Crew Cab DD
    2002 Grand Prix GTP. 40th Anv edition, 3.8L Supercharged V6, 130$ BBQ special. 111,000k
    1999 Chevy Silverado 350 5.7L vortec z71, 299k miles, Built 350 Built 4l60E slow wip
    1997 Grand Prix GTP, 3.8L supercharged V6 -Knocking motor mod. 189,000k
    1995 BMW 325I Slow, old, and high tech.

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    Lurker Captain Ficho's Avatar
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    Re: Why is my car using so much gas?

    on average, all highway I get 25 in my LQ1
    DD's:
    1997 Volvo 850 wagon - 265k miles - T5 turbo, 5spd, awd... 1 of 214

    Toys:
    1987 Buick Grand National - 71k miles - Show car/garage queen... 426whp
    1995 Pontiac Grand Prix GTP - 181k miles - built LQ1... turbo 3800 coming soon.

  7. #7

    Re: Why is my car using so much gas?

    Check the basics:

    Tire pressures.
    Air filter.
    PLugs (state of tune).
    DRIVING HABITS (even a good run of fuel econ can be badly skewed by one top speed pull.........don't ask how I know ).

    Oh.........and here's one...........was it windy??

    Even a crosswind can fuck up fuel econ very nicely.



    And finally...........even E10 ethanol gas can hurt 3-4% as compared to regular 87 octane.
    1999 Dodge Neon R/T: Is MINE now.........WTF?? Maybe I DO have a working car for autoxing after all!<br /><br />1997 Honda Prelude SH: Still going tap-tap, and still being abused......8000rpm is good for it, I SWEAR.<br /><br />1993 Nissan Sentra SE-R: The parts and organ donor has appeared but has yet to be used.<br /><br />1992 Nissan NX2000: Rusting quietly while I try to figure out if a Bluebird long-block is really worth it.<br /><br />1991 Pontiac Grand Prix: Currently in 4th gear due to a shift-cable malfunction, but I&#39;m so lazy it may NEVER get resurected AGAIN.

  8. #8
    Breakdown's Avatar
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    Re: Why is my car using so much gas?

    Quote Originally Posted by 19Cutlass94
    Recently I drove like 390 all highway miles, and i only got 25mpg... on straight highway! I mean maybe it was because it was going like 70-75 some of the time, but that cant be the whole reason as to why. Is it possible I might have an injector thats stuck open or leaking? Would i be able to test this by ohm testing the injectros or no?
    That really sounds par for the course to me. Did you used to get lots better?

    My picks - if you did.

    Catalytic converter or EGR.

    Most likely cat, when was the last time that was replaced (if it was?)


    BREAKDOWN ABILITIES: In car mode, his engine emits vibration that causes mechanical failures in other vehicles...can speed to 200 mph...uses concussion cannon in robot mode.
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    If it took me 7-14 hours to change an alternator, I'd set the car on fire and roll it down a hill.
    . . .then I'd set myself on fire.

  9. #9
    Addicted to eaton's Avatar
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    Re: Why is my car using so much gas?

    my car 97 gtp 3800 supercharged V6

    Highway
    75mph 30mpg
    65mph 34.5-35.5
    mpg 55 45-55 mpg

    In town
    20-23mpg

    my avg
    26.3
    2010 Chevy Silverado 325 5.3L Vortec Z71 Crew Cab DD
    2002 Grand Prix GTP. 40th Anv edition, 3.8L Supercharged V6, 130$ BBQ special. 111,000k
    1999 Chevy Silverado 350 5.7L vortec z71, 299k miles, Built 350 Built 4l60E slow wip
    1997 Grand Prix GTP, 3.8L supercharged V6 -Knocking motor mod. 189,000k
    1995 BMW 325I Slow, old, and high tech.

  10. #10

    Re: Why is my car using so much gas?

    Quote Originally Posted by Anthony
    my car 97 gtp 3800 supercharged V6

    Highway
    75mph 30mpg
    65mph 34.5-35.5
    mpg 55 45-55 mpg

    In town
    20-23mpg

    my avg
    26.3
    What's that, based off your trip computer?


    Jay, 25 MPG for 70-75 is a little but under what it should get, but remember you're still un-tuned. Even though your PCM fuel trims show it's "alright" there's more to be had by getting it tuned. With my stock L82 PCM I couldn't pull greater than 22 MPG on my commute, but after tuning I range from 24-26 consistently and that was after simple fuel adjustment and timing advancement. Also remember the 3.33 FDR will stop you from hitting much higher at those speeds. The W-bodies with the factory 3400's usually had 2.84's and that's one of the ways they were rated so high on the highway. When I drop my speed to the ~65 mph range, I realistically see around 28 MPG.



    Yeah, it's still on the road. 219,982 mi


  11. #11
    19Cutlass94's Avatar
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    Re: Why is my car using so much gas?

    Quote Originally Posted by Brian P™
    Quote Originally Posted by Anthony
    my car 97 gtp 3800 supercharged V6

    Highway
    75mph 30mpg
    65mph 34.5-35.5
    mpg 55 45-55 mpg

    In town
    20-23mpg

    my avg
    26.3
    What's that, based off your trip computer?


    Jay, 25 MPG for 70-75 is a little but under what it should get, but remember you're still un-tuned. Even though your PCM fuel trims show it's "alright" there's more to be had by getting it tuned. With my stock L82 PCM I couldn't pull greater than 22 MPG on my commute, but after tuning I range from 24-26 consistently and that was after simple fuel adjustment and timing advancement. Also remember the 3.33 FDR will stop you from hitting much higher at those speeds. The W-bodies with the factory 3400's usually had 2.84's and that's one of the ways they were rated so high on the highway. When I drop my speed to the ~65 mph range, I realistically see around 28 MPG.
    yeah I guess that makes more sense to me now that I think about it like that. I just thought that I should be getting more than that. Im gonna try to slow down to ~65-66 on the highway and not punch it to get around slower cars on the backroads. I wanna try and get it close to ~28 or so, then Id be happy. But when I hooked up the AFR, it read the correct fuel trims, ok well more correctly speaking the correct AFR, for what it should be. Even though its untuned. WOT it dips down to 12.5AFR. It just seems like the 93 in my car goes a little bit faster than it should be.
    Jay

    1994 Oldsmobile Cultass Supreme SL
    3400/Getrag 284 5spd
    1995 Chevy K1500 350c.i. 5spd Z71
    350/NV3500 5spd
    2014 Chevrolet Malibu LS
    Stock - Daily Driver

  12. #12

    Re: Why is my car using so much gas?

    you're a richer guy than me I stick with strictly 87 octane laced with ethanol. I have enough fun filling the F-body tank with premium.

    Do you get any knock retard running 87?
    Yeah, it's still on the road. 219,982 mi


  13. #13
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    Re: Why is my car using so much gas?

    A Post So I Can Follow This Thread
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  14. #14
    BXX's Avatar
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    Re: Why is my car using so much gas?

    Quote Originally Posted by Brian P™
    you're a richer guy than me I stick with strictly 87 octane laced with ethanol. I have enough fun filling the F-body tank with premium.

    Do you get any knock retard running 87?
    After seeing your timing maps, how the hell do you get away with using 87 and seeing no KR??? Hell, I see KR with 89
    -08 Kia Spectra SX -2.0L BetaII/Auto
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  15. #15

    Re: Why is my car using so much gas?

    because of my cam. There is a lot of valve overlap and duration which causes #1 natural exhaust gas recirc; #2 lower dynamic compression.
    Yeah, it's still on the road. 219,982 mi


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