A nice note about driving with an automatic - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 39 (permalink) Old 02-04-2009, 07:24 PM Thread Starter
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A nice note about driving with an automatic

Hey guys,
I've been doing a small experiment for mileage after I discovered a nice feature with the auto trans.
When Driving, the TC will lock above 45ish mph. this is nice for the transfer of power, but it creates some serious drag when you let out.
I've found that simply tapping the brake pedal (just enough to light the Brake light) will do one of two things:
1: unlock the TC
2: upshift
Either way, rpms drop to just barely above idle. this reduces the drag and allows you to coast further on the energy you've used getting to speed.
I didn't think much of it until I looked at my EGT gauge and realized that when I did this, the engine was still in Deceleration fuel cutoff mode- meaning I was coasting further, and still coasting without using fuel.
In my rather brief log of mileage, before this test, my tank mileages have ranged from 16.15-17.38, with an average of 17.18.
In testing this over the last two fillups, i've noted mileages of 17.45 and 18.27 respectively.
I'd probably be getting better, but it's at least once a day that I nail it from a stop and test my 0-60
thought I'd share the numbers with ya.
I'm expecting better as I get better at using this technique.
Dan

Dan
96 Powerstroke: 6637, downpipe to dump exhaust, 140v IDM and a shift kit.

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post #2 of 39 (permalink) Old 02-04-2009, 09:09 PM
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Re: A nice note about driving with an automatic

Nice Dan, thanks for the tip.

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post #3 of 39 (permalink) Old 02-04-2009, 09:14 PM
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Re: A nice note about driving with an automatic

Thats a cool tip. Thanks
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post #4 of 39 (permalink) Old 02-04-2009, 09:24 PM
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Re: A nice note about driving with an automatic

i've done that for awhile it really helps alot

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post #5 of 39 (permalink) Old 02-04-2009, 10:10 PM Thread Starter
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Re: A nice note about driving with an automatic

No problem guys, I like to help when I can
I'll have a third fillup's data in 3-4 days.

Dan
96 Powerstroke: 6637, downpipe to dump exhaust, 140v IDM and a shift kit.

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post #6 of 39 (permalink) Old 02-05-2009, 01:41 PM
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Re: A nice note about driving with an automatic

Dan

You are 100% correct! I have been playing with this for over a year
now with good results.

I had a tc lock switch that is never used. I now use it as a momentary
switch to bump the tc off. It removes a good bit of engine braking. The
TC will stay unlocked so long as the IVS is activated.

When you let out of it sometimes you get a second rise in rpm (your #2).
Its not a shift of anything. Its the motor braking with the coast clutch.
Some of the old obs pcm codes will turn off the coast clutch with od off.
With it off, you will see the motor go into idle mode and no motor braking
at all. The later pcm codes have coast clutch allway's on until the trans
is in 4th (od). Its just the trans strategy. You can manually unlock the
coast clutch for further gains.

Bill

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post #7 of 39 (permalink) Old 02-05-2009, 01:49 PM
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Re: A nice note about driving with an automatic

great info ill be trying it for sure....... thx

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post #8 of 39 (permalink) Old 02-05-2009, 04:28 PM
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Re: A nice note about driving with an automatic

Ok, here is a ringer.

My 2003 Jetta TDI when you are declerating in gear ( it is a standard 5 speed), shuts off all fuel until you get to about 1200 rpm and then it slowly feeds idle fuel back in. My 1989 F-150 4.9 ( C-6 auto) does the same thing until about 1200 rpm.

What does this PCM do while the engine is deceleration in lock up? Does it inject idle fuel, no fuel or what ever it wants to do?

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post #9 of 39 (permalink) Old 02-05-2009, 04:43 PM Thread Starter
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Re: A nice note about driving with an automatic

Jon- Deceleration fuel cutoff mode is the same in these as in your others. I don't know the exact Rpm, but I guess it's somewhere around 900-950.

Bill-Thanks for the full explanation on how it works.
I've also noted that with the IVS activated, and the truck slowly decelerating, it will continue to downshift with the TC unlocked... and maintain the state of no fuel injected and maximum coasting time Edit: you said this is the coast clutch engaging? Is this what you were refferring to when you said "you will get a second rise in rpms"?

Getting off the freeway, I let off the skinny pedal, tap the brakes, and coast for almost half a mile down the goofy off ramps around here. I don't hear the idle until i'm down to 20mph or so.

Dan
96 Powerstroke: 6637, downpipe to dump exhaust, 140v IDM and a shift kit.

84 Honda Sabre V65 1100: pipes, jet kit and new tires. Faster than I think I'll ever need.
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post #10 of 39 (permalink) Old 02-05-2009, 06:30 PM
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Re: A nice note about driving with an automatic

Quote:
Originally Posted by secondarychaos View Post
Getting off the freeway, I let off the skinny pedal, tap the brakes, and coast for almost half a mile down the goofy off ramps around here. I don't hear the idle until i'm down to 20mph or so.
Its because its engine braking from the coast clutch.
If you turn off the coast clutch you get no engine braking.
Its the same feeling as throwing the trans in netural.
Next time you get off the exit throw it in netural and you
will see how much further you will go. That is how it will
feel without the CC.
It can be hard on the brake system at times.

Bill

97 Quigley 4X4 PSD
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