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-   -   DFSO (deceleration fuel shut off) strategies and explanations (https://www.focusfanatics.com/forum/mk3-focus/281522-dfso-deceleration-fuel-shut-off-strategies-explanations.html)

GoShockers 03-06-2012 07:38 PM

DFSO (deceleration fuel shut off) strategies and explanations
 
Hey friends,

I'm looking to find out every thing I can about the DFSO system in my new Focus. I have done some searching on this forum and have found bits and pieces, but perhaps a single thread on the topic can combine all the knowledge this forum holds into one place.

I am trying to create some hypermiling strategies and would like to know the speeds at which DFSO turns on and when it turns off. Also, I like manually turning on the AC button when I am coasting to the light and turning it off when the light turns green. I want to know if having the AC on as I am coasting down to the light will keep the DFSO from activating.

Thanks in advance!

csvt2060 03-06-2012 08:14 PM

Best way to do this is with a scangauge and look at the closed/open loop status. On mine the DFSO would work with or without A/C and it would stay activated upon coast down until ~25MPH.

GoShockers 03-07-2012 12:24 AM

Quote:

Originally Posted by csvt2060 (Post 4044227)
Best way to do this is with a scangauge and look at the closed/open loop status. On mine the DFSO would work with or without A/C and it would stay activated upon coast down until ~25MPH.

Thanks for the data point. And I realize that owning a scangauge is the way to go but not all of us have one of those. I was about to purchase an ultra-gauge until I learned of the battery drain problem.

Perhaps those with scanguages and technical knowledge on the DFSO system could share their knowledge in here so we all benefit. Can a person "feel" when the DFSO is activated?

Visioned 03-07-2012 07:46 AM

I have a scangauge, if you tell me what to look for I can get the data for you.

Altis 03-07-2012 09:25 AM

Quote:

Originally Posted by GoShockers (Post 4044156)
..........Also, I like manually turning on the AC button when I am coasting to the light and turning it off when the light turns green. I want to know if having the AC on as I am coasting down to the light will keep the DFSO from activating.

Thanks in advance!

Just a heads up, doing this very frequently is actually quite hard on the actuator for the A/C. Whatever money you're trying to save on brakes by doing this, you may end up paying 10x for new A/C parts. [poke] Rather than using cheap brake pads, you're using an expensive climate control component to slow the car down.

DarinS 03-07-2012 11:59 AM

Quote:

Originally Posted by Altis (Post 4044977)
Just a heads up, doing this very frequently is actually quite hard on the actuator for the A/C. Whatever money you're trying to save on brakes by doing this, you may end up paying 10x for new A/C parts. [poke] Rather than using cheap brake pads, you're using an expensive climate control component to slow the car down.

I think he's trying to save on fuel, not brakes. But this is a very good point. You could never in a million years save enough fuel by activating/deactivating the A/C on decel to make up for the $1500 it will cost to replace the compressor and/or EM clutch.

BetaDnB 03-07-2012 12:24 PM

The way I understand this system is the fuel system shuts down any time you're coasting in gear with no accelerator use. Since it's in gear the rolling of the tires keeps the engine cranking.

kam327 03-07-2012 12:36 PM

Quote:

Originally Posted by BetaDnB (Post 4045341)
The way I understand this system is the fuel system shuts down any time you're coasting in gear with no accelerator use. Since it's in gear the rolling of the tires keeps the engine cranking.

The thing I can't wrap my head around with this is that if there's no fuel being injected then there's no combustion in the cylinders while coasting - wouldn't the engine sound be much different while coasting? Even no engine noise at all or just some kind of mechanical whirring sound?

GoShockers 03-07-2012 12:58 PM

Quote:

Originally Posted by Altis (Post 4044977)
Just a heads up, doing this very frequently is actually quite hard on the actuator for the A/C. Whatever money you're trying to save on brakes by doing this, you may end up paying 10x for new A/C parts. [poke] Rather than using cheap brake pads, you're using an expensive climate control component to slow the car down.

I always heard that turning the AC button off and on was the same as the compressor cycling which it does continually when in use. Did I receive incorrect information? I did it a million times in my 2001 Focus and the engine died (thrown rod at 150k) before the air conditioner ever did.

GoShockers 03-07-2012 01:03 PM

Quote:

Originally Posted by Visioned (Post 4044812)
I have a scangauge, if you tell me what to look for I can get the data for you.

Thanks!

Do you notice the DFSO activating only at particular speeds; for example, only after decelerating from 50mph but not 40mph? Or does it turn on as long as your foot is off the gas and you are over 25mph? Also, have you ever seen it on under 25mph? And have you found the 3 second delay after lifting off the gas to be true in your experience?


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