J. Sweet: 740 rpms cruising?

Discussion in 'Volvo 740' started by geronimo, May 3, 2007.

  1. geronimo

    geronimo Guest

    Well, I finally drove the 92 740 turbo wagon enough to get a MPG
    figure. Not good....16 mpg, mostly highway speed. The kickdown cable
    has been adjusted to where the tranny does shift into high gear (at
    first it wouldn't). THe turbo is working perfect, the engine runs
    really smooth! But I am thinking it may still be turning more revs
    than its supposed to, making it eat gas. At 60 mph, it is turning
    2500 rpm. That is an awful lot more revs than my 88 Camry turns! I
    know the O/D has kicked in, as when I hit the button on stick, it revs
    up to 3500. A spare tranny came with the car, but no telling if it is
    REALLY a good tranny, as the motorheads (not good ones as it turns
    out--- since they assembled engine without crank pulley key) claim it
    is. Replacing a tranny is beyond what I would want to tacke myself,
    and probably too expensive to have done, so if it is a tranny issue
    making the MPG bad, then I need to buy a replacement car that gets
    near double that. On the other hand there is possibility the car is
    running too rich....but it seems that if the control system was
    out-of-wack, then I would get a check engine light. How could I test
    for a rich condition without one of those sensors you stick up the
    tailpipe? I recently had the fuel rail up to check each injector, and
    all are fine, none are stuck open, and none leak. Should I maybe
    change O2 sensor and PCV valve and see if that helps MPG? I hope it is
    an engine issue---- not tranny, as I can do something about that, and
    possibly not cost much. thanks, Geronimo
     
    geronimo, May 3, 2007
    #1
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  2. As you accelerate, do you hear and see the shifts from first to second, and
    from second to third? You may have to disable OD to verify that.

    Mike
     
    Michael Pardee, May 3, 2007
    #2
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  3. geronimo

    James Sweet Guest


    Mine runs about 2200 RPMs as I recall crusing at 60 MPH, it has an M46
    manual gearbox and gets 25-26 MPG on the highway and about 18 around town.
    Something is still screwy if you're only getting 16, I've gotten that low
    once but I was really thrashing it and mostly around town. With the slushbox
    you should be getting 22 or so highway and around 17 in town.
     
    James Sweet, May 4, 2007
    #3
  4. geronimo

    geronimo Guest

    Well, it definitely shifts into third. 1st to second is perfect, and
    automatic....however, you have to let the car wind up to abt 3400 RPM
    in second, then you have to let off the gas a little to get it to
    shift into third. If you don't let off the gas a little when it should
    shift, it never will shift into third. You can make it shift into
    third at a lower RPM, but because of the load on the engine, it won't
    want to stay in third as you are getting up to hwy cruise speed.
    Since my 740 turbo wagon doesn't have the manual gearbox, it
    probably has a different RPM for hwy speeds. (Man, I wish it did have
    manual shift!) Hopefully I can figure out some way to determine if its
    running rich, as I need to rule that out as a factor.
    I have tried putting more slack in the kick-down cable, but it did
    not help with the third gear shifting.

    Thanks, Geronimo
     
    geronimo, May 4, 2007
    #4
  5. geronimo

    James Sweet Guest


    Well you could convert it to manual, I've done that to a couple Volvos and
    it's pretty straightforward so long as you can find a donor car at a wrecker
    with all the parts you need.
     
    James Sweet, May 4, 2007
    #5
  6. geronimo

    Shawn Guest

    I'd guess that the torque converter isn't going into lockup. That is of
    course if a 92 740 has a lockup torque converter?

    Shawn
     
    Shawn, May 5, 2007
    #6
  7. geronimo

    James Sweet Guest

    Even so, it should still do better than 16 mpg, that's pretty bad.
     
    James Sweet, May 5, 2007
    #7
  8. geronimo

    Perk Guest

    Hi all,

    I've been watching this thread so, out of curiosity, when I went on the
    the freeway today I kept an eye on my mph/rpm on my 1990 740 GLE (B234F
    non-turbo) with auto trans and I got about 2500 RPM at 65 and about
    2800/2900 at 70.

    My average MPG has consistently been just a little bit below 24, perhaps
    23.8 overall.

    All the best,

    Perk :)>)
     
    Perk, May 6, 2007
    #8
  9. geronimo

    geronimo Guest

    Gee, thats not all that different.....at 65, mine (its turbo model) is
    doing about 2700rpm, only around 200 rpm faster.

    I don't have a clue whether the tranny is lock-up type or not, and
    whether there is some external circuit/relay that could be at fault.
    I don't think I have seen any electrical control circuits for tranny
    in either the Haynes or Chiltons manuals. Anyone know?

    Wonder if there are automotive shops that have those exhaust gas
    analyzers? I think those anayzers can show percent O2 and thus
    indication of rich or lean mixture. In Texas they are scarce I think,
    as you don't have to have an emissions test....or at least not where I
    am in Texas. I can at leaast see that there is not a puddle of fuel
    below the exhaust piple after it runs a while, and it doesn't smell of
    fuel, either. The exhaust is normal/ clear.

    At such a poor mileage figure, with gas price very high, it just
    doesn't pay to keep the car, it would actually *save* money to pick up
    payments on a mid-90s manual toyota or Camry. But I have invested so
    much time and money (like brand new set of tires) into it already.

    thanks, Geronimo
     
    geronimo, May 6, 2007
    #9
  10. geronimo

    Shawn Guest

    This
    http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM-2244&N=700+115&autoview=sku

    plus this

    http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM-3375&N=700+115&autoview=sku

    will give you real time indication of your air/fuel mixture. If you can
    determine which is the signal wire from your O2 sensor, you would just need
    the gage.

    Shawn
     
    Shawn, May 6, 2007
    #10
  11. geronimo

    James Sweet Guest


    Could always do the shotgun approach. Replace the O2 sensor, rear coolant
    temp sensor, remove the injectors and have them tested/cleaned and if fuel
    consumption is still high try swapping the AMM with a good used one.

    Don't forget also the possibility of a fuel leak.
     
    James Sweet, May 6, 2007
    #11
  12. geronimo

    geronimo Guest

    Well, that is an expensive means to find out mixture. Not $$$ for that
    now. Seems to me if I just tapped into the signal wire from the
    existing O2 sensor, and read it with a D.M.M., I could see what the
    mixture is. The problem is tht I would have to have a chart to
    interpret the voltage reading, and I don't know if such a chart is
    available on internet. I think it is millivolts?


    Hey James: I was thinking that the sensor connector under the intake
    manifold toward the FRONT was the one feeding signal to the ECU, and
    the conn. behind it, towards the REAR, was for the gauge in inst.
    cluster. Have I got it backwards? I am finding some bad connectors,
    as the rubber insulation that holds the pins in place inside the
    connectors has hardened and crumbled from age/heat.
     
    geronimo, May 7, 2007
    #12
  13. geronimo

    geronimo Guest

    James:

    (see earlier post first) Well, I pulled both temp sensor
    connectors off one at a time, and you are right----the one driving the
    gauge is in front. But something strange. Eiiither one, when
    disconnected, sets the CHECK ENGINE light on! This could not be
    unless both temp sensors tie in to the ECM. But why would the sensor
    for the gauge be tied in also? And it seems to be bad. THe temp
    gauge NEVER goes above mid-scale, no matter how overheated the engine
    becomes. (There were a couple of steaming overheats before we realized
    there was this problem with it). When I swapped in a whole new inst.
    cluster trying to fix the speedometer problem, the temp gauge still
    did not go above mid-scale, so that is why I think the sensor is bad.
    When I saw that a new sensor would cost around $40, I just got me a
    whole new temp gauge and sensor for $15.00, and rely on that now.
    But since it sets the check engine light also, maybe it could have an
    adverse effect on performance/gas mileage?

    It seems a little odd for a thermistor to fail like this....increasing
    or decreasing its resistance to a certain point, and then not an ohm
    further. If it is a negative coefficient thermistor, then maybe
    there is an abnormal external resistance, and it cannot go lower than
    that?
     
    geronimo, May 7, 2007
    #13
  14. geronimo

    James Sweet Guest


    Usually when the sensor fails, it goes open circuit. You should be able to
    find one at a junkyard, I've never paid more than $2 for one. IIRC they're
    about $20 online brand new.
     
    James Sweet, May 7, 2007
    #14
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