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Mileage dropped significantly. Any recommendations? 850

Hi,
I used to get 17 - 19 mpg local and 25 - 29 mpg on highway with my 1996 volvo 850. I was very happy with that considering many problems brickboarders have suffered.
After my car hit 120,000 miles, a couple of check engine lights have turned on. First it turned out to be aif flow mass. My mechanic didn't do anything and the light disappeared once he reconnected the battery. I didn't see any significant change in mileage at that time. Second was rear oxygen sensor. While I drove the volvo with the light on, I noticed that highway mileage dropped to 20 or so, which never happened before. A mechanic asked me whether I noticed a change in my mileage and I said yes. I was told that I will get my usually mileage back once the oxygen sensor was replaced. I, though, didn't see any significant improvement yet. Well, I have to admit that I didn't do anything special such as fuel injection cleaning, replacing plug, wire, etc. for the last 5 years or so. I did it when I bought the car with the mileage of 70,000 back in 2001. That was the last time. I though changed air filter and oil filter regularly and kept the tire at the right pressure and so forth. Any suggestions I might try to get my mileage back would be greatly appreciated. Thanks.








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    Mileage dropped significantly. Any recommendations? 850

    A fair number of 850 owners have had problems with stuck caliper pistons and dragging brakes which would probably affect your mileage. Also I remember, although this may be a 740 issue, someone mentioning that auto parts stores have the wrong O2 sensor listed for the 850. They all use the same computer system so it wouldn't matter which one was used. Just another thing to concider.








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    Mileage dropped significantly. Any recommendations? 850

    I would also reccomend checking all of the Engine Vacuum Lines (Rubber Elbows), there is a good article on volvospeed.com covering this. I have just used rubber vacuum hose from the auto parts store but the elbows are cheap from volvo also. here is the link (I hope)for locations of lines. http://www.volvospeed.com/volvo_performance.php. just scroll down to the proper info. Good luck, bob








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      Mileage dropped significantly. Any recommendations? 850

      this link only brings you to the startup page, wou need to click on repairs and maintence and proceed. http://www.volvospeed.com/volvo_performance.php








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    Mileage dropped significantly. Any recommendations? 850

    Thank you so much for your kind tips from the three contributors. I will make sure to change the Front Oxygen Sensor and the others (plugs, wires, rotors, etc.) as suggested. I will let you know guys know what happens after that. Thank you again.








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      Mileage dropped significantly. Any recommendations? 850

      If you haven't bought a front 02 sensor yet, let me recommend http://www.autohausaz.com/ I bought one from them a few months ago (direct fit bosch) for about $100...by far the cheapest place. For the wires, don't go bosch, but bogicord. People are havning bookoo's of issues out of the bosch wires. For plugs, I recommend (even for turbo's) volvo's own, or bosch plain coppers...much cheaper and you don't have detonation issues like folks are having with platinunm plugs. These last items can be bought from fcpgroton.com for less than other places. Good luck and let us know how things turn out. Oh yeah, and gap your plugs at .028.
      --
      1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.








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    Mileage dropped significantly. Any recommendations? 850



    Your front O2 sensor may be dying also. They often fail slowly so don't turn on the CEL right away. When mine went, mpg fell from ~20 around town to 12. Was running so rich the exhaust fumes would choke a horse and the bumper area was black with soot. Changed it and mpg went back to normal

    bl








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      Mileage dropped significantly. Any recommendations? 850

      I agree...was surprised that the rear 02 sensor was replaced before the front one. Think this is the first time I've ever heard of this. I suspect the front one needed replacing more than the rear and thus your issue.
      --
      1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.








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    Mileage dropped significantly. Any recommendations? 850


    I would say start with new plugs, wires, distributor cap and rotor. The wires might still be ok, but what the heck.

    Best of luck and let us know what helped or didn't help.

    --
    '97 850 n/a Wagon, 130K mi







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