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Thread: Subie newbie from MD

  1. Top Of Page | #11
    goldfingerfif's Avatar

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    Re: Subie newbie from MD

    Quote Originally Posted by Ace View Post
    What kind of information is the fuel trims giving me and what should I be looking for?


    Sent from my iPhone using Tapatalk
    I monitor different things depending on what I'm doing but then again I also tune my own car with Cobb AccessTuner.

    As far as fuel trims the information it is giving you is the percentage of correction to obtain a stoichiometric air:fuel ratio based on O2 sensor feedback in comparison to the calculated value it expected to use.
    What's the expected value? Final Injector Pulse Width.

    Final IPW (Injector Pulse Width) (microseconds) = Final Fuel Multiplier × Fuel Injector Scale × Load × (A/F Corr. #1 + A/F Learn #1 ) × Per Cylinder IPW Comp. × Small IPW Comp.


    Final Fuel Multiplier = 1 lamda in closed loop operation or is an interpolated value looked up in the Primary Open Loop Fuel Table. (You can monitor "Closed Loop Switch" to see when it is in closed or open loop...closed loop mean it corrects fuel based on sensor feedback, open loop is solely calculated and it doesn't matter how much it deviates from the value you want to obtain as no correction is applied)
    Fuel Injector Scale = IPW (in microseconds) for stoichiometric fueling per gram of calculated load. This is a single value and comes from a table, it would basically only be changed if you change injectors or fuel type.
    Load (in grams/revolution) = Calculated load and can be monitored via access port. It is calculated, and equals Final Mass Air Flow (MAF Voltage converted to interpolated value air value in grams per second + load compensation. Load compensation = % looked up in 2 tables based whether TGV's are open or closed and uses Manifold Absolute pressure and RPM as the Axis) ÷ RPM × 60 (To convert RPM to RPS..rev per second)
    Per Cylinder IPW Comp. = Small correction from lookup table to fix injector flow difference or fuel flow characteristics, harmonics, etc.
    Small IPW Comp. = From lookup table and is a flow correction provided by injector manufacturer generally to correct injector not linear behavior when IPW is small (generally under 3 milliseconds)
    A/F Correction = Short term or immediate correction, ECU wants this to be 0
    A/F Learn = Long Term Correction and are based on the average A/F Correction to an extent and there are a few different areas of load these apply. You can also monitor these values on the AccessPort under A/F Learn A, A/F Learn B, etc.

    What you would be looking for is a large value or percentage as that can be an indicator of a problem ie bad gas, sensor, vacuum leak, boost leak, PCV oil blow by, etc.

    Feedback Knock is immediate correction if knock is detected / heard (when certain conditions are met) and is equivalent to A/F correction as the ECU wants this to stay 0
    Fine Knock Learn is long term correction if Feedback knock is continually detected within certain table value based on calculated load and rpm to preemptively retard timing to prevent Feedback Knock from occurring and then slowly adds timing back over time testing to see if it is safe again in case of bad gas for example.

    Air Intake temp is measured at the MAF sensor and it will indicate air flow problems for example if it is 40deg out but it is reading 140 while cruising there might be a problem or something you might want to upgrade to correct or explain why the car feels sluggish if you were to mash the gas, though it can get higher after idling on a hot day for a while, etc. In general I find it mostly useless, much more useful if placed after intercooler which is where mine is and not recommended to do so unless you change to speed density tune like my car is setup to be on, reason being is it isn't there to correct for the air temp as MAF measures air mass directly, the point is as a correction to the MAF sensors calibration due to temperature.

    Dynamic Advance Multiplier - It should always be at 1 and is used to calculate additional timing as specified in the dynamic advance (2 tables depending if TGV's are open or closed) table that is added to the Primary Ignition Value. Dynamic Advance Timing (4 tables TGV open, normal and AVCS Warm-Up, TGV Closed, normal and TGV Warm-Up) and is calculated as such dynamic advance table value * DAM (Dynamic Advance Multiplier). Generally regarded as bad if it drops below 1, I rarely if ever monitor this.

    Last edited by goldfingerfif; 1 Week Ago at 06:25 PM. Reason: Bolding any text would let me post

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  3. Top Of Page | #12
    Track Monkey Grinder34's Avatar

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    Re: Subie newbie from MD

    Quote Originally Posted by goldfingerfif View Post
    I monitor different things depending on what I'm doing but then again I also tune my own car with Cobb AccessTuner.

    As far as fuel trims the information it is giving you is the percentage of correction to obtain a stoichiometric air:fuel ratio based on O2 sensor feedback in comparison to the calculated value it expected to use.
    What's the expected value? Final Injector Pulse Width.

    Final IPW (Injector Pulse Width) (microseconds) = Final Fuel Multiplier × Fuel Injector Scale × Load × (A/F Corr. #1 + A/F Learn #1 ) × Per Cylinder IPW Comp. × Small IPW Comp.


    Final Fuel Multiplier = 1 lamda in closed loop operation or is an interpolated value looked up in the Primary Open Loop Fuel Table. (You can monitor "Closed Loop Switch" to see when it is in closed or open loop...closed loop mean it corrects fuel based on sensor feedback, open loop is solely calculated and it doesn't matter how much it deviates from the value you want to obtain as no correction is applied)
    Fuel Injector Scale = IPW (in microseconds) for stoichiometric fueling per gram of calculated load. This is a single value and comes from a table, it would basically only be changed if you change injectors or fuel type.
    Load (in grams/revolution) = Calculated load and can be monitored via access port. It is calculated, and equals Final Mass Air Flow (MAF Voltage converted to interpolated value air value in grams per second + load compensation. Load compensation = % looked up in 2 tables based whether TGV's are open or closed and uses Manifold Absolute pressure and RPM as the Axis) ÷ RPM × 60 (To convert RPM to RPS..rev per second)
    Per Cylinder IPW Comp. = Small correction from lookup table to fix injector flow difference or fuel flow characteristics, harmonics, etc.
    Small IPW Comp. = From lookup table and is a flow correction provided by injector manufacturer generally to correct injector not linear behavior when IPW is small (generally under 3 milliseconds)
    A/F Correction = Short term or immediate correction, ECU wants this to be 0
    A/F Learn = Long Term Correction and are based on the average A/F Correction to an extent and there are a few different areas of load these apply. You can also monitor these values on the AccessPort under A/F Learn A, A/F Learn B, etc.

    What you would be looking for is a large value or percentage as that can be an indicator of a problem ie bad gas, sensor, vacuum leak, boost leak, PCV oil blow by, etc.

    Feedback Knock is immediate correction if knock is detected / heard (when certain conditions are met) and is equivalent to A/F correction as the ECU wants this to stay 0
    Fine Knock Learn is long term correction if Feedback knock is continually detected within certain table value based on calculated load and rpm to preemptively retard timing to prevent Feedback Knock from occurring and then slowly adds timing back over time testing to see if it is safe again in case of bad gas for example.

    Air Intake temp is measured at the MAF sensor and it will indicate air flow problems for example if it is 40deg out but it is reading 140 while cruising there might be a problem or something you might want to upgrade to correct or explain why the car feels sluggish if you were to mash the gas, though it can get higher after idling on a hot day for a while, etc. In general I find it mostly useless, much more useful if placed after intercooler which is where mine is and not recommended to do so unless you change to speed density tune like my car is setup to be on, reason being is it isn't there to correct for the air temp as MAF measures air mass directly, the point is as a correction to the MAF sensors calibration due to temperature.

    Dynamic Advance Multiplier - It should always be at 1 and is used to calculate additional timing as specified in the dynamic advance (2 tables depending if TGV's are open or closed) table that is added to the Primary Ignition Value. Dynamic Advance Timing (4 tables TGV open, normal and AVCS Warm-Up, TGV Closed, normal and TGV Warm-Up) and is calculated as such dynamic advance table value * DAM (Dynamic Advance Multiplier). Generally regarded as bad if it drops below 1, I rarely if ever monitor this.

    Awesome info.


    Check out my journal here!

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  5. Top Of Page | #13
    On a quest of STi erudition! Alin's Avatar

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    Re: Subie newbie from MD

    @Ace , what made you decide to get an STi over any other car on the market?
    @goldfingerfif , thanks for all of the information! Even I need a refresher every now and then.


    Quote Originally Posted by Batmobile_Engage View Post
    It doesn't have to have a nut on the outside. Many are short, but I often try to find long ones that sometimes have a bend in them.

  6. Top Of Page | #14
    Basic Member Ace's Avatar

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    Re: Subie newbie from MD

    Quote Originally Posted by Alin View Post
    @Ace , what made you decide to get an STi over any other car on the market?
    @goldfingerfif , thanks for all of the information! Even I need a refresher every now and then.
    Wanted a fun car and it needed to be 4 doors. dad mobile status!


    Sent from my iPhone using Tapatalk


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