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  1. #1

    How does ECU know when to adjust timing?

    OK, I know there are fuel maps and ignition curves etc, but how does the ECU know when to change/adjust timing when in and out of boost at dif throttle positions?...

    ie: if you have less boost, do you have more timing? and vice versa?

    Does temperature of incoming air play a role in these ecu changes?...PR...


  2. #2
    Site Admin Green Hulk's Avatar
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    It makes changes via sensor input.

    manifold air pressure
    air temperature
    crank timing/rpm's
    throttle position, etc.

  3. #3
    SplishSplash's Avatar
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    Ok, I'll have to explain a bit to lay this out.

    The way it works is when you connect the layard and before you press start, the ECU read the MAP sensor in the intake maifold to get the baseline atmospheric pressure. This gives the ECU starting parameters
    Once the engine is started, the ECU gets signals from the Thorttle position sensor which tell the ECU where the throttle is and also logs where it was so it knows rate of change so it calculates how much and fast your moving the throttle.
    The ECU knows engine RPM from a crank sensor at all times.
    The ECU gets manifold pressure/vaccum reading from the MAP sensor.
    The ECU also knows intake air temp from the air intake sensor in the intake manifold.
    The ECU takes all the inputs from the above sensors (TPS,MAP,IAC,CPS,Coolant sensor,etc) and using what it gets, adjust the fuel injector duty cycle and spark timing advance and retard.
    There is no O2 sensors in the exhaust so it cannot tell if it lean or rich, it just goes by maps in the ECU directed by the input of the above sensors. It runs in an "open Loop" mode all the time (closed loop requires O2 sensors)
    Basically the ECU gets inputs and based on those, adjusts what it thinks is best based on those inputs.
    Performance ECU's change the maps to provide either more aggressive timing advances or more fuel or both. But emisions would go up too.
    Stock ECU's can adjust to modifactions as long as they fall into its maps, once you go outside the maps capabilities, you get fault codes or wose lean conditions and boom.

  4. #4
    SplishSplash's Avatar
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    or just what Jerry said..

  5. #5
    Site Admin Green Hulk's Avatar
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    very well said splish splash

  6. #6

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    Quote Originally Posted by SplishSplash
    Ok, I'll have to explain a bit to lay this out.

    The way it works is when you connect the layard and before you press start, the ECU read the MAP sensor in the intake maifold to get the baseline atmospheric pressure. This gives the ECU starting parameters
    Once the engine is started, the ECU gets signals from the Thorttle position sensor which tell the ECU where the throttle is and also logs where it was so it knows rate of change so it calculates how much and fast your moving the throttle.
    The ECU knows engine RPM from a crank sensor at all times.
    The ECU gets manifold pressure/vaccum reading from the MAP sensor.
    The ECU also knows intake air temp from the air intake sensor in the intake manifold.
    The ECU takes all the inputs from the above sensors (TPS,MAP,IAC,CPS,Coolant sensor,etc) and using what it gets, adjust the fuel injector duty cycle and spark timing advance and retard.
    There is no O2 sensors in the exhaust so it cannot tell if it lean or rich, it just goes by maps in the ECU directed by the input of the above sensors. It runs in an "open Loop" mode all the time (closed loop requires O2 sensors)
    Basically the ECU gets inputs and based on those, adjusts what it thinks is best based on those inputs.
    Performance ECU's change the maps to provide either more aggressive timing advances or more fuel or both. But emisions would go up too.
    Stock ECU's can adjust to modifactions as long as they fall into its maps, once you go outside the maps capabilities, you get fault codes or wose lean conditions and boom.
    Sorry, but stock ECU has no maps. It`s a P.R.O.M. (not your date either) Program Read Only Memory that set the ECU value`s (parameter`s)
    The ECU only activate`s retard when the knock sensor has signal input.
    This type of EFI is called Speed Density (no O2 sensor)
    Your pretty close with your analogy.

  7. #7
    Awesome answers guys, can we save this thread to somewhere here???...PR...

  8. #8
    SplishSplash's Avatar
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    Actually Green Monster is is based on maps, maps that are stored in the PROM (Programmable read only memory) and its probably a EEPROM b ecause it can be flash updated by the dealer if required.
    Service manual word for word "Signals from sensors are used by the ECM to determine the injection parameters(Fuel Maps) required for optimum a-fuel ratios .. and...The ECM is programmed with data (it contains ignition mappings) for optimum timing under all operating conditions"
    The ECM listens to its sensors and uses thier input to calculate what map to use.

  9. #9

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    Quote Originally Posted by SplishSplash
    Actually Green Monster is is based on maps, maps that are stored in the PROM (Programmable read only memory) and its probably a EEPROM b ecause it can be flash updated by the dealer if required.
    Service manual word for word "Signals from sensors are used by the ECM to determine the injection parameters(Fuel Maps) required for optimum a-fuel ratios .. and...The ECM is programmed with data (it contains ignition mappings) for optimum timing under all operating conditions"
    The ECM listens to its sensors and uses thier input to calculate what map to use.
    Sound`s like some fishy/flashy jargon to me....
    And yes, if you can flash it that make`s it an EEPROM

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