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Thread: DFCO explained measured and how to utilize it

  1. #1
    Senior Member MightyMirageMpg's Avatar
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    DFCO explained measured and how to utilize it

    DFCO is an acronym for "deceleration fuel cut off"

    It's programming in the engine computer that allows the fuel injectors to turn off anytime the car has enough momentum to turn the engine at a runable speed.

    How does the car drive the engine?
    The engine and tires are physically linked in a manual transmission car anytime the transmission is in gear and the clutch pedal is not pushed in. If the car is moving forward and you take your foot off the gas, the car is now driving the engine with its momentum.

    So what's it mean?
    Your not injecting fuel and saving money

    Why bother measuring it?
    Because another member (eggman) and I both noticed the same thing. Odd readings from scan gauges when coasting vs dfco. - Not every car is equipt with dfco. I do not believe it would show up on EPA testing, so the car manufacture has little to no reason to add it. - i have read some cars have DFE (deceleration fuel enleanment)

    How to measure it?
    A multimeter set to dc hz measurement, with the test leads PARALLEL to across the load. This measurement gives you the amount of injection cycles over a period of 1 second

    i stuffed wires into my injector connector. Done, easy. Just be careful because if you short the wires your car will suffer some sort of damage.


    Results:

    This thing DFCO's like a mother.... From any RPM down to approximately 1200 rpm. I did not notice any "not until warm" or any other charactoristics.

    What did i learn?
    The ultragauge is simply incorrect in its readout when DFCO is happening.
    I've been driving wrong this whole time coasting with the clutch in up to stoplights
    Im a nerd

    Pictures explained:

    1- warm idle

    2- 2nd gear full throttle full rpm ( was a bit higher bad photo time i think it hit 58)

    3- wired into injector

    4- DFCO happening


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    Last edited by MightyMirageMpg; 04-21-2017 at 05:16 PM.

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    2of9 (04-26-2017),Eggman (04-21-2017),Fit (04-25-2017),poorman1 (04-23-2017),Pryme (04-21-2017),Top_Fuel (04-21-2017)

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    Senior Member Top_Fuel's Avatar
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    Quote Originally Posted by MightyMirageMpg View Post
    What did i learn?
    The scangauge is simply incorrect in its readout when DFCO is happening.
    I've been driving wrong this whole time coasting with the clutch in up to stoplights
    I have a Scangauge and also noticed that when coasting (with my manual transmission in neutral), I often see the instant MPG reading quicky jump from maybe 250mpg to 9999mpg...which I always assumed meant DFCO. But if I'm coasting in neutral...how is my engine still turning with no injector pulse? Hmmm...something isn't right...

    So what you are saying is this...

    If you want to take advantage of DFCO, you have to coast with the transmission in gear regardless of what the Scangauge is reading.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.6 mpg (US) ... 22.0 km/L ... 4.6 L/100 km ... 62.0 mpg (Imp)


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    I am pretty sure I get the 9999 in neutral and coasting in gear.

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    Senior Member MightyMirageMpg's Avatar
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    Quote Originally Posted by Top_Fuel View Post
    So what you are saying is this...

    If you want to take advantage of DFCO, you have to coast with the transmission in gear regardless of what the Scangauge is reading.
    Exactly

    Quote Originally Posted by Pryme View Post
    I am pretty sure I get the 9999 in neutral and coasting in gear.
    I have the ultra-gage and it shows what i would expect for regular coasting mpg when dfco.

    I wish i knew about the differences before purchasing but when i was looking them up i didn't find anything like this

    Either way, measuring the fuel injector directly is obviously the best way to tell what's really happening for making tweaks to things.

    I updated the initial post to correct wrong information

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    Senior Member Top_Fuel's Avatar
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    Google "Scangauge DFCO". Looks like this topic has been discussed on a few other forums...and the Scangauge anomaly with DFCO seems to be a known limitation with the device.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.6 mpg (US) ... 22.0 km/L ... 4.6 L/100 km ... 62.0 mpg (Imp)


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    Moderator Eggman's Avatar
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    Quote Originally Posted by MightyMirageMpg View Post
    How to measure it?
    A multimeter set to dc hz measurement, with the test leads PARALLEL to across the load. This measurement gives you the amount of injection cycles over a period of 1 second
    Great idea. I wonder if your Fluke would capture Min/Max/Avg for this? I like how the dial labeling is worn off!

    Also, I wonder if there is a way to log this through the OBDII port. Hm...

    Quote Originally Posted by Top_Fuel View Post
    Google "Scangauge DFCO". Looks like this topic has been discussed on a few other forums...and the Scangauge anomaly with DFCO seems to be a known limitation with the device.
    I'm not sure it's just ScanGauge because my OBDLink LX does it too, which makes me think it's related to how the onboard ECU monitors things. I also relate this to a greater error between my calculated MPG and what my MID B registered for my last tank. I'll get another chance to check this on my next fill-up.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.6 mpg (Imp)


  8. #7
    Bikerfreind
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    I drive the by looking forward.
    Can I coast to a intersection while in gear I would definitely do so because the engine breaks and it shuts off the fuel to the engine.. So I save money in the last end. If I go down hill and there is a red light I just switch to a lower gear and coast down..

    I know trucks in Europe have a feature where you can keep the exhaust gas inside the exhaust, and kind of stop the engine, this way you get even more out off the used fuel and you save money on the breaks.

  9. #8
    Senior Member MightyMirageMpg's Avatar
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    Quote Originally Posted by Top_Fuel View Post
    Google "Scangauge DFCO". Looks like this topic has been discussed on a few other forums...and the Scangauge anomaly with DFCO seems to be a known limitation with the device.
    Well now I know

    Quote Originally Posted by Eggman View Post
    Great idea. I wonder if your Fluke would capture Min/Max/Avg for this? I like how the dial labeling is worn off!

    Also, I wonder if there is a way to log this through the OBDII port. Hm...

    I'm not sure it's just ScanGauge because my OBDLink LX does it too, which makes me think it's related to how the onboard ECU monitors things. I also relate this to a greater error between my calculated MPG and what my MID B registered for my last tank. I'll get another chance to check this on my next fill-up.
    I don't think my meter can record anything and its too expensive to leave wired up in the car.

    Great observation. I never dfco much before, and my display was near spot on. I'll have to retest once I get used to driving correctly. Did your display usually read high or low?

    Quote Originally Posted by uheym View Post

    I know trucks in Europe have a feature where you can keep the exhaust gas inside the exhaust, and kind of stop the engine, this way you get even more out off the used fuel and you save money on the breaks.
    It's almost worth installing engine brakes on a mirage just for the looks you would get Rollin into town lol




    I put my test equipment on the mivec oil feeder control valve and I think I can replicate the signal and alter it. Unfortunately I don't have an oscilloscope but the way it's wired I don't think it's needed. (Switched negative) I'm not sure if this is a good idea or not, but poking around EVO forums they are convinced simply unplugging it (full cam advance) yields mpg gains. So why not play... i ordered a $4 diy frequency meter I'm going to solder up and wire in permanently, and also a 555 timer and everything to make a pulse generator. More to come, the riskier engine damaging stuff later in the summer.

  10. #9
    Moderator Eggman's Avatar
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    Quote Originally Posted by MightyMirageMpg View Post
    I don't think my meter can record anything and its too expensive to leave wired up in the car.
    It can - it's just limited. Refer to page 4: Fluke Models 175, 177, 179 True RMS Multimeters Users Manual

    Quote Originally Posted by MightyMirageMpg View Post
    Did your display usually read high or low?
    Usually high, as in optimistic. I've been tracking each tank since purchase and averaging the results. Details can be found in my fuel log entry for Speck.

    Quote Originally Posted by MightyMirageMpg View Post
    I put my test equipment on the mivec oil feeder control valve and I think I can replicate the signal and alter it. Unfortunately I don't have an oscilloscope but the way it's wired I don't think it's needed. (Switched negative)
    Do you think the oil feeder valve control signal is digital? I would expect it to be analog as it won't respond as fast as an injector.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.6 mpg (Imp)


  11. #10
    Senior Member MightyMirageMpg's Avatar
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    To my understanding the oil feeder control valve works similar to a servo on an rc car, it's sent 12 0 12 0 12 0 12 to average 6 or halfway or however it needs to break the signal up for to get its average voltage and position

    While I'll never know the pulsewidth, i can monitor its actual position via the ultragage so assuming i make a variable PWM i don't see why i couldn't control it? I'm only looking to nail down 1 position (anything i can gain at freeway cruise)

    I'm not exactly the most tech savy individual so if someone sees me making an obvious error... By all means point it out


    Last edited by MightyMirageMpg; 04-23-2017 at 10:55 AM.

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