Help '87 Volvo 740 Turbo terrible gas mileage only on highway or freeway ?

Discussion in 'Volvo 740' started by circuit slave, Jun 19, 2006.

  1. I have an '87 Volvo 740 Wagon which I dread getting on the freeway for.
    It seems like I'm getting 10 mpg on the freeway at speed limit of 65.
    I'm not even using the turbo. When the throttle TPS sensor became
    defective, it was like this, so I replaced it, but it's still using up
    a lot of gas.

    Is it logical to think that because I'm giving it more acceleration,
    that more gas would be used?
    I don't smell fumes when driving or stopping. It's like 5-10mpg on the

    I replaced the O2 sensor which was full of carbon and black, but it
    hasn't seemed to help. I replaced spark plugs and replaced the air
    filter. It's just ridiculous--I can see the guage going down little
    by little as I'm driving on the freeway. It's as if I can't go
    anywhere unless it's by street lights taking forever to get there, but
    at least I'm not using up so much gas.

    Maybe the catalytic converter? I do hear something rattling sometimes
    when I'm driving, but I'm not sure if it's that or not. Any help,
    circuit slave, Jun 19, 2006
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  2. circuit slave

    Jamie Guest

    did you ever replace that wiring harness that was giving you so much
    trouble? perhaps something electronic controlling your fuel mixture
    and/or ratio is shot. I hope someone else will chime in, but you posted
    in February all of the problems you had with your wiring harness.

    Jamie, Jun 19, 2006
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  3. No, not yet. I know, I know. I really need to get that fixed. On a
    side note, it does idle like it's cold (kinda shaking) when I'm at a
    stop. I'll look into that harness wiring. I just haven't been able to
    come across it recently at a decent price. I'll look into that.

    I will say this, though, It hasn't died one me once yet : ) like it
    used to. I isolated the shorts which were causing it to die, at least.
    circuit slave, Jun 20, 2006
  4. circuit slave

    James Sweet Guest

    Well replace or rebuild the wiring harness first, until you do that
    you're just chasing your tail.
    James Sweet, Jun 20, 2006
  5. circuit slave

    Jamie Guest

    Contact Dave Barton. I can't tell you his prices at this very moment,
    but I know that there are times when he has harnesses for around
    $100-$130. Sometimes he has some in decent order that require minor
    repairs and he can sell these cheaper.

    You can always e-mail him and ask to be put on a "waiting list" for a
    $100 harness.

    Good luck.
    Jamie, Jun 20, 2006
  6. circuit slave

    hjsjms Guest

    A malfunctioning turbo caused poor milage on my daughter's Saab.
    hjsjms, Jun 20, 2006
  7. circuit slave

    hjsjms Guest

    Shaking at an idle could be from a lot of things, including a vacuum
    leak, bad valves, etc. You should really have the car looked at by
    someone with the proper diagnostic equipment rather than guessing and
    swapping out parts.
    hjsjms, Jun 20, 2006
  8. circuit slave

    User Guest

    You need to carefully check all the hoses running from the MAF to the
    intake manifold. One of them has a split or blow out on the bottom. Any
    air leak at all between the MAF and the intake manifold will cause the
    fuel injection to be very rich. As a side note if the green wire from
    the O2 sensor is horted to ground the system will go full rich.

    User, Jun 20, 2006
  9. I'll check all hoses, thanks everyone. As far as having it looked at a
    Volvo mechanic or someone with experience and the equipment---I'll
    first invest in that wiring harness first---I know that is something
    that does NEED replacing. Thanks for all the replies, and suggestion,
    people ! : )
    circuit slave, Jun 21, 2006
  10. circuit slave

    James Sweet Guest

    I rebuilt my existing harness by splicing new wires into the old
    connectors and putting heatshrink tubing over everything. Took a lot of
    patience and I was freezing my butt off in January doing it but I had to
    get the car back on the road and it worked.
    James Sweet, Jun 21, 2006
  11. freezing your butt off in January sounds about right this time of year
    ( the West Coast is warming up right now).
    circuit slave, Jun 22, 2006
  12. circuit slave

    Jamie Guest

    Come on up to Northeast Texas - a cool 100 degrees. Thank goodness for
    low humidity and this drought. Dust held my old harness together for I
    think the last 6 months. I think in some places the wires rotted out
    and the electricity had to arc to make a connection.

    Damn tough cars!
    Jamie, Jun 22, 2006
  13. circuit slave

    James Sweet Guest

    Yuck, we're pushing up into the high 70's here off and on, figure I'll
    have to start running the AC later this week.
    James Sweet, Jun 24, 2006
  14. circuit slave

    Jamie Guest

    High 70's? We call that a "cold front." LOL

    We're about to go into water restrictions - serious drought here. I
    moved here 1 year ago and if we've gotten 10 days of rain in that time
    I'd be surprised.

    I'll be happy when fall rolls around. My wife and 5 year old son are
    ready for some camping.
    Jamie, Jun 24, 2006
  15. Once when I lived in Phoenix my wife and I were doing a Cub Scout thing
    outdoors the first weekend in Spring... the temperature hit 101 degrees.
    Only four months there have not recorded 100 degrees: November through
    February. My wife and I married in the middle of the longest unbroken run of
    temperatures above 110F recorded there: 21 days. Most of those days were
    115F and above.

    I'm so glad to be in Flagstaff now, where the summer temperatures are
    flirting with 90 degrees in the hottest part of the day.

    Mike, the reformed desert rat
    Michael Pardee, Jun 24, 2006
  16. circuit slave

    wblakesx Guest

    I had some suspicions about a BMW Motronic harness. It was easy to
    split open to trace the doubtful wires. There's lots of ways to stich
    it up again.
    wblakesx, Jun 26, 2006
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