Civic bad Mpg help

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  • Kyle

    Needs More Cowbell!
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    4   0   0
    Feb 24, 2011
    2,969
    31
    Hill Country
    Howdy guys.. I have a problem that is leaving me a bit perplexed...

    When I first got my '01 civic, I was making 34-36 mpg running 75-80 mpg. Then I got new wheels and tires. Went from the factory 14" steely to a 15inch. Tire size went from 185 70r14 to a 195 65r15. Not a big difference at all. I didn't see much (if any) loss in mileage when I made the change. My speedometer reading is off by up to 3 mph on the high end. My odometer is now off by 1 mile for every 40 miles driven. I compensated for that when calculating mileage.

    As it stands, I just put 700 miles on my car, all hwy and I made 27mpg. It seems to have been slowly declining to the point that it just pisses me off now.

    This car only has 112k miles. The engine has new plugs (10k miles ago), I have a very small oil leak at the valve cover, clean throttle body, new filter... The engine runs awesome. I'm not throwing any codes either.

    I'm at a loss. I'm thinking I may need to replace the o2 sensors since I appear to be running rich... I could be wrong... I disconnected the battery and let the computer reset, checked my plugs (the look new still)... I can't find anything, at least not obvious. So now I'm frustrated...

    Suggestions would be wonderful.
     

    rls210

    New Member
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    0   0   0
    Jul 12, 2013
    17
    1
    San Antonio
    Check with the tire manu, and compare the number of revs per mile between your old set and your new set. Tire stagger could be off. A 3 mph diff is a surprising number of tire revs per mile. At one time I raced SCCA road races in a CRX and had to keep a 14 inch tire but was able to change from a 185/60 to a 205/55 and keep the same tire rpm's, with-in 3 rpm's per mile. Also check valve lash and throttle position sensor. You will probably have to have a dealer check the TPS.
     

    rsayloriii

    TGT Addict
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    0   0   0
    May 11, 2009
    3,314
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    H-Town, TX
    At 112k it is due for o2 sensors.

    If they're running correctly, no need to replace them. Get you a scan tool and read the o2 sensor readings. A factory repair manual will tell you the range the o2 sensors should be reading.

    Playing "CALL OF DUTY IX: DOUGHNUT WARRIOR" does not make you a "cop". -wakal
     

    Kyle

    Needs More Cowbell!
    Rating - 100%
    4   0   0
    Feb 24, 2011
    2,969
    31
    Hill Country
    Check with the tire manu, and compare the number of revs per mile between your old set and your new set. Tire stagger could be off. A 3 mph diff is a surprising number of tire revs per mile. At one time I raced SCCA road races in a CRX and had to keep a 14 inch tire but was able to change from a 185/60 to a 205/55 and keep the same tire rpm's, with-in 3 rpm's per mile. Also check valve lash and throttle position sensor. You will probably have to have a dealer check the TPS.


    It's been progressively getting worse. Like I said, there was little to no change in mpg after the wheel/tire change.. It's only recently (last 3 months or so) that I have been having noticeably bad mileage. But I will give all that a check. I have an OBD scanner that works with a tablet app that has been great for diagnosing and tracking changes in almost everything
     

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