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Thread: ECO Mod: Howto reduce level of enrichment when cold

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    ECO Mod: Howto reduce level of enrichment when cold

    The situation: When the cold engine is started, the fuel/air mixture is enrichened by adding extra fuel. The colder, the richer. This is to make the car more driveable, so it won't sputter and shake, won't conk out, and also to get the catalyst warmed up quicker.

    The problem:
    There is generally a quite bit more enrichment than really necessary. A bit less would save lots of fuel during warm-up.
    Now, we can't re-program the ECU for that, but there is something else that can be done! If the ECU gets informed by the coolant sensor that the engine is a little warmer than it actually is, it will produce less enrichment and save gas. However, when the car is warmed-up, the sensor must tell the ECU the correct temperature.

    How is this done?
    The coolant temperature sensor is a simple NTC. Most cars use this method. The resistance of the NTC increases when cold, and decreases when hot.
    The Mirage sensor has about 2500 Ohms at 20′C / 72′F, around 180 Ohms at boiling point, and about 15 000 Ohms (15K Ohms) at -20′C.
    With this mod, a second sensor is added via a series resistor of 2700 Ohms. The series resistor is of the same resistance as the temp sensor at room temperature. This resistor is to make the sensor-circuit report the correct temperature when the engine is approaching, and when it has attained normal warmed-up state.
    See circuit diagram for details. The two added parts are on the top part of the diagram.

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    I got the second sensor at a junk yard. It is electrically identical to the original sensor, but mechanically of somewhat different shape and size.

    Below is a photo of the secondary sensor with plug and wires, soldered onto a copper bracket. The copper was a junked piece of a copper water pipe, soldered onto it for the sake of better heat conductivity:

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    Ideal would be to use the same type coolant temperature sensor the Mirage came with, but this one perfectly serves the purpose.
    The original sensor is installed on the left side of the cylinder head, and although it is fastened on the head, most of it is immersed in coolant. You can find it between the engine and the battery. There is one brown, and one sky blue wire attached to it by a removable plug. In the following photo, it would be in the far right, but can not be seen here because there is other stuff in front of it. The new second sensor is in the middle of the photo.
    The second sensor was soldered to a copper bracket and bolted onto the cylinder head. That ensures ideal heat conductivity, because the second sensor needs to report engine temperature correctly, just as the original one.

    Note: a strong and heavy soldering iron is needed for soldering the sensor to a copper bracket! That way, the sensor does not have to suffer from high soldering temperature too long. After soldering, be sure to check the sensor electrically, because too much soldering heat can wreck it. Check there is no internal conductivity between the connectors and the case.
    It was then fastened to the cylinder head where it seemed convenient. Thus it can be assumed it has and reports the same temperature as the coolant and the original sensor.

    The second sensor is connected by a plug/jack, its two wires leading to the two wires of the original sensor via the 2700 Ohms series resistor. See circuit diagram. All wiring was put neatly into the cable assembly. All of the new electrical connections and the resistor were perfectly insulated. The cable assembly looks like it has been manufacturered that way, and not been touched since.

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    Note: There has been a recall in the USA to reprogramme the ECU for reduceing the way too excessive enrichment of the cold engine. If they offer it for your car, go get it done!

    This mod will not just somewhat reduce enrichment when cold, but also further reduces excessive enrichment during the entire warm-up period and thus saves fuel. I have have not had any driveability issues whatsoever. In Europe, the above mentioned recall was not offered.

    The fine print:
    1) As usual, everything at your own risk.
    2) If you are not used to work with a soldering iron, or not used to working with electrics/electronics, or have not much notion or little experience with car electrics, please don't do this yourself!


    FYI here the electrical curve of the second temp sensor, being electrically identical to the OEM sensor.
    Based on the info from above, a knowledgeable person could if they wanted recalculate this mod and exactly understand what it does:
    Name:  coolant sensor properties.jpg
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    Edit:

    See the table Eggman calculated and added in post number 18.
    It clearly shows the modified coolant temp as reported to the ECU.
    Thanks Eggman!


    EDIT UPDATE:

    Tried different values for the series resistor in my 1.0L Mirage, and this is what happens:

    At 2.500 Ohms everything is fine.

    2000 Ohms also works well.

    1750 Ohms or less is no good, because the radiator fan will come on too early during warm-up with the radiator still being cool and the thermostat closed. Remember, this car has only one single temperature sensor for everything!

    To sum it up:

    1) any value between about 2500 and 2000 Ohms is fine.

    2) This mod goes much further than the reprogramming of the ECU (USA recall) for enrichment reduction.

    3) My car is a 1.0L without(!) EGR valve. Yes, the 1.0L engine without AS&G is sold in Europe without EGR, but the 1.0L with AS&G does have EGR.

    I think using valve-overlap is maybe how they keep NOX down at testing-relevant revs and load levels, unless they VW their way out to get better figures...


    Last edited by foama; 12-01-2018 at 10:00 AM.

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    Daox (12-01-2018),Eggman (05-17-2016)

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    Interesting. What changes have you noticed while using this setup?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.7 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.7 mpg (Imp)


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    Quote Originally Posted by Eggman View Post
    Interesting. What changes have you noticed while using this setup?
    What I have noticed?
    During warm-up, the display shows less fuel being consumed.
    The normal stabilized consumption level, or normal warmed-up consumption level, is being reached earlier.
    Very shortly before reaching warmed up temperature, the revs in idle can be a little bit lower, but almost unnoticeable.
    To put it short, it saves considerable fuel during the warming-up phase. The colder, the more savings, and this is most noticeable during short distance driving.

    Btw: This works with almost every engine, regardless of make...

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    Eggman (05-18-2016)

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    Thanks for your reply. How does your car drive with this modification? Do you notice any difference in how it runs?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.7 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.7 mpg (Imp)


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    Nice mod. but can the engine run lower than 750 rpm when warmed up, if no, why? I used obd to show me the fuel consumption at idle when warmed up, it was about 0.6 liters/ hour. not bad if it is true...

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage Intense 1.2 manual: 47.9 mpg (US) ... 20.4 km/L ... 4.9 L/100 km ... 57.6 mpg (Imp)


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    Also, how about using a thermal switch that disconnects the new circuit when the engine reaches operating temperature?

    I'm curious to know what coolant OBD reports with this modification. Is there any chance you could collect some data on this for some operating cycles?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.7 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.7 mpg (Imp)


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    Quote Originally Posted by Eggman View Post
    Also, how about using a thermal switch that disconnects the new circuit when the engine reaches operating temperature?

    I'm curious to know what coolant OBD reports with this modification. Is there any chance you could collect some data on this for some operating cycles?
    Due to putting a resistor in series with the second sensor, the temperatur (Ohms) reported to the ECU is correct when warmed up. Thus no difference when warmed up, and no need for a thermal switch.

    If you want to calculate it, take the resistance-to-temp curve from the first post. The Ohm at a given temp is reported to the ECU, which understands ohms as temperature.
    From that you can see what a particular ohms-value means in temperature. This is for the unmodified Mirage.


    Compare the values of the unmodified to the modified circuit like this:


    To calculate the modified circuit: Consider R1 to be the original single sensor. The temp/Ohm values of the original sensor (R1) are shown in the table.
    The additional sensor R2 has the value of (R1 + 2500 Ohms). Both sensors are assumed to be at the same temp.
    The modified circuit consists of R1 (the original sensor) parallel to (R2 + 2500 Ohms).
    For each temperature of interest, calculate these new temp/Ohm values, and compare them to the original unmodified circuit containing only R1. The difference between modified and unmodified circuit is shown as the difference in Ohms. See the table for how much Ohms means how much temperature being reported.

    The formula for the resistance of the modified circuit goes like this:

    R1 = original sensor. (Characteristics Ohm-versus-temp are in the table on the bottom of the first post.)
    R2 = second sensor, (having same Ohm-value as original R1) plus 2500 Ohms for the resistor in series.
    That can be written like this:


    R1 x (R2 + 2500 Ohms)
    ----------------------------------- = resistance of the modified circuit at a given temperature.
    R1 + ( R2 + 2500 Ohms)


    That formula gives the Ohms value of the entire modified circuit at a particular temperature.
    Compare the value of the equation with only the value of the original sensor R1 (the unmodified circuit) and you have the difference.
    Last edited by foama; 05-18-2016 at 09:12 AM.

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    No thank you. Have a great day.

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    Senior Member Cobrajet's Avatar
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    Ironically, US market Mirages have an open recall to correct this very thing.

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    Quote Originally Posted by Cobrajet View Post
    Ironically, US market Mirages have an open recall to correct this very thing.
    And that's great. A flash or component replacement by the manufacturer is fine.



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