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Old 04-13-2011, 11:52 PM   #31 (permalink)
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Ok so I think my only question that didn't get answered, is how the heck do I know when I'm in DFCO?

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Old 04-14-2011, 12:21 AM   #32 (permalink)
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To go into DFCO, you have to be in closed loop, in gear, engine above the minimum rpm programmed into your car's ECU, and TPS dropped to idle speed.

When you're in DFCO, your ECU sets open loop and shuts off the fuel injectors. You can tell you're in DFCO by monitoring open/closed loop and TPS on a Scangauge or Ultragauge. Scangauge will also show DFCO by raising mpg to 9999 if you have the cutoff setting properly preset.
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Old 04-14-2011, 02:41 AM   #33 (permalink)
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Quote:
Originally Posted by justjohn View Post
Ok so I think my only question that didn't get answered, is how the heck do I know when I'm in DFCO?
The only absolute way is to have some sort of instrumentation (for example: scangauge, ultragauge, mpguino).

If you don't have instrumentation, one thing I notice with my car though (1994 acura integra manual, using MPGuino) is when im coasting down and in gear, the MPGuino will show instant mpg as 99999, meaning im currently in DFCO. If i step on the gas again, it feels like my car "jerks" back to life, and there is a slight delay to when the car starts accelerating normally. It's very subtle though.

If I am coasting down in gear but NOT in DFCO (ie, in a high gear but low speed), and then i step on the gas, the car accelerates smoothly.

Hope this helps.

When you're ready to downshift
1)step on the clutch
2) at the same time: blip the throttle/shift your gear lever
3)step off the clutch

voila! Simple eh? There is no wear on the engine when you blip the throttle because the clutch is disengaged.
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Old 04-14-2011, 08:38 AM   #34 (permalink)
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Originally Posted by justjohn View Post
I think there must be some fundamental flaw in my understanding of the system though, because rev-matching seems counter-intuitive in terms of wear to me.
It isn't, for the reasons you gave below :

Quote:
"It's not using the clutch when RPMs are high that's hard on it, it's when there is a large difference between where the engine speed is and where it 'should' be for whatever gear you're going to."
Rev-matching is really necessary when you're downshifting pretty hard , i.e. when going fast.
When you're downshifting a much slower speeds, the differences in rotational speed are also lower.

Downshifting into 1st or 2nd gear however, is always best done using rev-matching, as these are very short gears.


Quote:
Cause when I learned that keeping on the gas during upshifting was bad for it, I originally assumed the logical link was simply "high RPM = bad for the clutch."
The smoothest way to shift up is to reduce the throttle when upshifting, rather than cutting it, so that when the clutch re-engages, the engine turns over at the rpm it'd normally do in the next gear at that speed.
It doesn't take much gas to do so.

Essentially, it's rev-matching again.
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Old 04-14-2011, 08:40 AM   #35 (permalink)
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Originally Posted by justjohn View Post
Ok so I think my only question that didn't get answered, is how the heck do I know when I'm in DFCO?
Do you have a fuel consumption display in the car ?


I've checked it on my car, it'll stay in DFCO until just over 1000 rpm when warm.
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Old 04-14-2011, 11:34 AM   #36 (permalink)
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I unfortunately do not yet have instrumentation. Thanks very much for all the great information though. I think I got everything I wanted to know plus a little more I didn't realize I needed.
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Old 04-14-2011, 11:39 AM   #37 (permalink)
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For the record, I don't downshift into 1st unless I'm using the engine to come to a complete stop...something else we wont discuss here, as it fits into the "driving without brakes" category, unless justjohn would like more information.
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Old 04-14-2011, 11:29 PM   #38 (permalink)
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I always want more information. :P

I think can guess the basic principals of that though, based on the things already said in this thread and simple logic just applied to fuel conservation.
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Old 04-15-2011, 12:07 PM   #39 (permalink)
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Quote:
Originally Posted by Christ View Post
If you have a manual, try keying off while braking down a hill. You won't lose p/s or brakes. If auto, try interrupting the injector circuit, and sitting them off manually while decelerating. If you don't physically feel a difference in engine drag, you're already in dfco.

Your LED may be lying, also. If you wired it to check for power, there's a good chance that it is. Most injection systems pulse/switch the ground side of the circuit (ecm input), with a constant power feed, often from some kind of distribution center.
If you turn the engine off, you will loose p/s. But I believe you'll get a pump or two of power brakes with the engine off. After that, it'll be a very hard pedal.
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Old 04-15-2011, 12:19 PM   #40 (permalink)
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The engine is still turning while you're engine braking, so even if you turn the key off, you'll still have both brakes and power steering.

And in case you're going to nit pick about the post not specifically referring to engine braking, re read the thread title.

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