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What could cause sudden low mileage on a car that seems to be running fine? 700

posted by  Thaddeus on  Fri Feb 21 15:11 CST 2003
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I can find no gasoline leaks.
I smell no gasoline in the exhaust.
The car idles normally.
It runs fine. No loss of power.
I don't think the brake shoes are dragging.
The injectors are 6 months old, the fuel pressure regulator 2 years old.
Any other ideas? I'm scratching my head.

thanks

Thaddeus







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    What could cause sudden low mileage on a car that seems to be running fine? 700

    uid 5153's pic
    posted by  Bishop on  Sat Feb 22 00:35 CST 2003
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    last visit: Wed Sep 5 04:11 CST 2007
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    I know that when the tappets are out you can notice increased fuel usage, but I have no experience with that in volvos.
    --
    Veronica, my 85 760Ti








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    What could cause sudden low mileage on a car that seems to be running fine? 700

    posted by  invar on  Fri Feb 21 20:39 CST 2003
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    last visit: Fri Feb 26 21:00 CST 2010
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    how much loss of mileage are we talking about here? and are you in a region where the fuel is oxygenated? it'll say on the gas pump at the station about so and so. they do it during the winters to reduce emissions or something. it does affect mileage though. i noticed about a 3-4 MPG drop on pure highway driving when they switched.
    --
    Kenric Tam
    1990 Volvo 740 base sedan (B230F)
    My Volvo 'Project'








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    What could cause sudden low mileage on a car that seems to be running fine? 700

    posted by  Rtilghman on  Fri Feb 21 17:26 CST 2003
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    Check anything that can affect mixture. Filters, AMM, KS, whatever... pay specific attention to wiring as well. You might also have gotten some poor gas if you buy cheap stuff. If its a turbo stick with 93... it's generally about $1 more for a full tank than 89/91, so there is no realy reason to go cheap.

    -rt








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      What could cause sudden low mileage on a car that seems to be running fine? 700

      posted by  Thaddeus on  Sat Feb 22 00:13 CST 2003
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      Yeah, I'm about to go down that road... replacing this and that until it works right..

      First I want to check the oxygen sensor. I had the exhaust from the cat back replaced about a month ago and that's when my wife noticed poor mileage. Maybe it got unplugged...

      All my cars get synthetic oil and premium gas. So bad gas shouldn't be an issue.

      Could it be a bad antiknock sensor?

      Puzzled. If it was way-rich, I should be able to smell it in the exhaust..








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        What could cause sudden low mileage on a car that seems to be running fine? 700

        posted by  mortoni on  Sat Feb 22 04:13 CST 2003
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        last visit: Fri Jan 30 03:51 CST 2009
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        It could well be the engine temp. sensor. It's resistance changes inversely to the change in engine block temperature. When cold the ECU senses a particular resistance value and lengthens the fuel pulse time of the injectors which enrichens the mixture. Check for a broken or detached wire lead on this temp. sensor. The temp. sensor could also be defective.







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