Vehicle feature that I didn't even know existed until I experienced it personally.

Discussion in 'General Motoring' started by Daniel Who Wants to Know, Mar 9, 2008.

  1. I have written about the '95 GC SE that I got recently before but I noticed
    a strange (to me) behavior that I had never heard of before. On an 86 mile
    round trip that I do twice a week I usually set the speed/cruise control for
    54MPH (55 speed limit) and I noticed that when I was going down a hill and
    the speed hit 60 that the trans downshifted to help keep my speed down. I
    had never been in a vehicle before that did this that I was aware of and the
    '92 Dynasty with the same engine and trans (3.3) didn't do it so it kind of
    surprised me a little and caused me to do a search and find the section of
    text I copied and pasted from the allpar site below about new features and
    driveline changes for '95. Anyway this feature just shows that although
    some people don't seem to like it much having an electronically controlled
    transaxle does have its perks as I can remember having to either step on the
    brakes (which cancels the cruise) or manually downshift going down some
    hills in other vehicles to keep my speed down. BTW so far by setting it at
    54 and maintaining my tire pressures I have a 21MPG average per the mini
    trip computer. Not sure how accurate it is yet but it seems to be fairly in
    line with how much gas I have used. This is despite the CEL/MIL being on
    with an EGR code because I need a new EGR valve assembly as moisture got in
    the electrical connector and corroded away one of the pins. (The Dynasty
    didn't have EGR)



    41TE Electronic 4-speed Overdrive Automatic - LeBaron Convertible, minivans:
    An automatic speed control overspeed reduction feature has been added to the
    transmission control software. It helps maintain vehicle speed at the
    selected set point when descending a grade. The TCM (transmission control
    module) first senses that the speed control is set. If the set speed is
    exceeded by more than 4 mph (6.5 km/hr) and the throttle is closed, the TCM
    causes the transaxle to downshift to Third gear. Subsequent to the
    downshift, the automatic speed control continues its normal operation. To
    assure that an upshift is appropriate after the set speed is reached, the
    TCM waits until the throttle is opened at least 8 degrees by the speed
    control system before upshifting to Overdrive again. If the driver applies
    the brakes, canceling automatic speed control operation with the transaxle
    still in Third gear, the TCM maintains this gear until the driver opens the
    throttle at least 8 degrees to avoid an inappropriate upshift. The upshift
    is also delayed for 0.5 seconds after reaching the 8 degree throttle opening
    in anticipation that the driver might open the throttle enough to require
    Third gear, thus avoiding unnecessary and disturbing cycling of the
    transmission. If the automatic speed control RESUME feature is used after
    braking, the upshift is delayed until the set speed is achieved to reduce
    cycling and provide better response.

    Additional refinements continue on the 41TE electronic four-speed automatic
    transaxle. For 1995, software changes provide smoother 2-1 low speed, heavy
    throttle downshifts. Kick-down shifts after a coast- down in Third are also
    refined.
     
    Daniel Who Wants to Know, Mar 9, 2008
    #1
  2. Daniel Who Wants to Know

    Bill Putney Guest

    It's a feature on the LH cars too - probably most car these days. It is
    generally helpful, but can be annoying in generally hilly terrain as you
    go down one hill and crest another (if anyone is familiar with hiway 460
    East of Lynchburg and Appomattox, VA, that is the exact worst-case for
    what I'm talking about).

    Also, if you have the cruise set just below ticket threshold for the
    straight-and-level, this will put you well over that on a long
    downgrade. I am in the habit (on two particular hills that I drive on
    my daily commute) of punching the 'Decel' button 3 or 4 times (drops
    cruise control setpoint 3 or 4 mph) just before the start of the
    downgrade to start that downshift earlier and stay safely below the 'get
    a ticket' threshold, and then to punch the 'Accel' button 3 or 4 times
    (ups the setpoint 6 to 8 mph) at the bottom for the long descent, then
    hit the 'Decel' button 3 or 4 times again when returning to straight and
    level to return to the original setpoint.

    This will never be a completely acceptable speed control augmentation
    for all terrains. If they programed it to hold the speed too tight, the
    constant up and downshifting would be very annoying on minor terrain
    variations. The way they have them set now works well for relatively
    level terrain. In constant short up/down hill, the constant shifting is
    annoying and does not hold speed well; on long grades, it allows way too
    much speed variation on hills if your goal is too travel just below the
    speeding ticket threshold on the level terrain using the same setpoint.

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    address with the letter 'x')
     
    Bill Putney, Mar 9, 2008
    #2
  3. Daniel Who Wants to Know

    Bob Shuman Guest

    21MPG seems low to me for 55MPH with a broken in 95, 3.3L and properly
    inflated tires. I have owned two grand caravans, a 1990 with a 3.3L and a
    heavier 1999 T&C with a 3.8L and both regularly got 26MPH on flat terrain at
    55MPH. Maybe this is because of the winter fuel mix that reduces gas
    mileage? I also do not know what you mean by "properly inflated" tires.
    Maybe you are using the door placard which I always thought was too low. (I
    keep my tires which have maximum inflation pressure of 35 PSI stamped on
    them at 32 PSI.)

    I have found that our 1999 3.8L T&C can actually get over 27MPG at a
    constant 50MPH. Mileage seems to drop as speed is increased...

    Bob
     
    Bob Shuman, Mar 9, 2008
    #3
  4. LOL I should have mentioned that while @ 54 the rest of the people pass me
    like I am sitting still so speeding tickets should be a non issue. The
    route is just 2 lane with some short slow lanes going up the hills but the
    strange part is that after tailgating me for a few miles rather than wait 10
    more seconds for me to get in the slow lane most people seem to pass me just
    as we are coming up on one. I guess I am the only one who values fuel
    savings over small time savings.
     
    Daniel Who Wants to Know, Mar 9, 2008
    #4
  5. Daniel Who Wants to Know

    Bill Putney Guest

    Well - the feature, with its ±4 mph window is perfect for you. No
    tickets for 60 in a 50.

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    address with the letter 'x')
     
    Bill Putney, Mar 9, 2008
    #5
  6. 21 is the combined not just the highway. I have seen 25MPG when I reset the
    mini trip readout while going down the highway. I am on Iowa 89 octane E10
    gas so that does reduce it a bit. The current tires are 35 PSI max cold so
    I can't go any higher than that but I plan to get a set of Nokian WRs soon
    so I can go higher on the pressures.
     
    Daniel Who Wants to Know, Mar 9, 2008
    #6
  7. Daniel Who Wants to Know

    Bob Shuman Guest

    Thanks for the clarification. I misunderstood that you were only getting 21
    on the highway at 55MPH. 25 sounds about right, although I do think you
    will do a little better in the summer.

    Bob
     
    Bob Shuman, Mar 9, 2008
    #7
  8. Daniel Who Wants to Know

    Nate Nagel Guest

    GM doesn't use this feature at least as recently as 2005. I got spoiled
    by my friend's Concorde which does.

    nate
     
    Nate Nagel, Mar 10, 2008
    #8
  9. Daniel Who Wants to Know

    Mike Y Guest

    My 96 Grand Caravan had this feature. It had the 3.8l motor. I was on
    a ski trip and had the cruise set and was surprised when it downshifted
    as I came down a mountain interstate. Overall, I really liked the feature.

    Mike
     
    Mike Y, Mar 10, 2008
    #9
  10. Daniel Who Wants to Know

    sdlomi2 Guest

    Bill, I was stopped by a patrolman on a July 3 a # of years ago for
    driving too slow. I'd just moved to a small S.C. town. Just left my dad's
    house and still daylite and hot, and the highway had a limit of 45. Not
    being in any hurry plus running my ac w/windows up and only going about
    40--gonna make a right turn shortly anyway, and about 3 cars accumulated
    behind, and 'here he came' with his lights flashing. Obviously he thought I
    was drinking, going so slow plus I was driving w/windows up in hot summer.
    He mis-accused me of weaving and even reached thru the door to my steering
    wheel asking what was wrong with the steering on my older, yet esp. nice '57
    Chevy. In later years after we became acquainted he admitted he'd never
    bothered had I been going 50 in that 45 instead of 40! ...or maybe if I had
    windows down, as he never dreamed that car old could have ac! We actually
    became friends. s
     
    sdlomi2, Mar 11, 2008
    #10
  11. Daniel Who Wants to Know

    Steve Guest

    "Grade management" is the general term. My wife's 93 Vision didn't have
    it originally, but picked it up during a re-flash pretty early in its
    life (I think the fact that I kept up with firmware updates on that car
    is what kept it out of the tranny shop until over 150k miles.

    It can be annoying as you said, but it beats the heck out of what my
    folks 84 Caddy did: On cruise, that thing would zoom 15-20 mph over the
    setpoint on downgrades and fall 10 mph below the setpoints on up-grades.
    The former was because the tall gearing provided no engine braking, the
    latter was because the HT4100 engine provided no torque :p
     
    Steve, Mar 13, 2008
    #11
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