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Old 07-29-2008, 08:44 PM   #1 (permalink)
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Auto transmission with the manual shift feature

So I have this manual shifting feature as part of my "automatic transmission." Would using this feature to find my most efficient cruise speed (lowest speed in highest gear) be a good tool for maximizing mpg? Or is there something about this manual shift feature that eliminates/decreases the perceived benefit of manual over automatic transmissions?

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Old 07-30-2008, 12:20 AM   #2 (permalink)
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My wife's VW Rabbit has this feature and I tried it a couple of times.
It kind of works, but it won't let you choose any gear you want. Let's say you want to shift into 5th doing 25, it just will not do it at this low speed. Basically I was constantly trying to get into higher gears.
You also have to push the shifter to the side, which makes it harder to shift into neutral for coasting.
I don't use it anymore whenever I drive her car, drive in D instead and can shift into neutral at any given time.
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Old 07-30-2008, 06:07 PM   #3 (permalink)
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I had an '07 Dodge Caliber and it had the same thing. It was almost worthless. It wouldn't shift smoothly and like what was said it wouldn't let you pick the gear you wanted if it was below a certain rpm range. Being able to shift into neutral is much more useful.
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Old 07-31-2008, 10:47 PM   #4 (permalink)
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There is such a feature on my 04 MB E320 4Matic. Like JustJoey described above, I can use the feature to urge the car to up shift to the 5th (OD) gear at, say, 50 kmph (instead of at a higher speed if I do nothing) in order to save some fuel.
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Old 06-17-2009, 01:50 AM   #5 (permalink)
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Hello -

It would probably be really hard to do, but it sounds like this is programmed into the ECU/PCM. In a perfect world, you would be able to REprogram the ECU/PCM to obey your shifting demands. I would make the only restriction to be based on the "minimum safe idle rpm", i.e. something like this :

Code:
new_drive_ratio = get_drive_ratio_from_shift_request( shift_up);

new_rpm = rpm_equation_from (  new_drive_ratio, current_mph, current_LOD);

if ( new_rpm > minimum_safe_idle_rpm )
{ // then 
    shift_gears( shift_up);
}
else
{
    ignore_driver_request();
}
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Old 06-17-2009, 08:32 AM   #6 (permalink)
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It's useful for highway driving in the 09 Honda Fit. The system in there does respond to your requests pretty well, and can be used to force shifts even when not in manual mode. Getting out of the low gears and into 3rd at about 25 mph is great for city economy. The transmission programming doesn't let you get into 3rd until ~30 normally.

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