How do engines detect higher octane fuel? - Page 4

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    #31
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    TheEnd's Car Details
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    The ECU will alter the fuel trims if it is out, but usually the advance tables are looked up via RPM and airmass, so advance is linked to airmass coming in, and the ECU sorts out the correct mass of fuel to add for that set airflow.
    There are tables of target lambda values (as in air/fuel ratios) and the lambda sensors are used to double check the fueling is correct, but it is a different branch to the ignition advance.
     
     

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    #32
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    Quote Originally Posted by TheEnd View Post
    Lambda sensors are going to have very little effect on octanes and ignition advance, they are treated separately.

    Almost all cars have knock sensors, but I remember the non vanos M50 was probably one of the last like that. Those had rigidly set advance, and they wouldn't pay attention to different fuels.

    Some newer engines like the E92 M3 now does knock detection with the spark plugs by ionising the gasses in the cylinder.
    Nowadays perhaps, its common place to have a knock sensor fitted, but this is still relatively new of many manufacturers, normally starting off with their performance models.

    Older vehicles that dont have knock sensors will only have the lambda sensor(s) to work from, bearing in mind, an OE ecu has a safe margin to work from. On older vehicles, youl find that using higher octane fuel will not give much performance advantage unless mapped on this fuel.

    To confirm, newer vehicles utilise the knock sensor, as has been stated above. You may also notice manufacturers quoting in brackets a different power output on brochures for running super unleaded. Different manufacturers do it in different ways, some have an additional map that is referred to under appropriate conditions.
     
     

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    #33
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    And also you have throttle position sensor to give the ecu a reading.
     
     

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