Load Sensing

Overview

The Engine Load may be measured in a variety of ways, such as using a Manifold Absolute Pressure (MAP) sensor (Boost Pressure), a Mass Air Flow (MAF) sensor, or a Throttle Position Sensor (TPS). Pedal position may also be used.

MAP or MAF may use Pedal as a backup should the primary sensor fail.

Scaling

The Load Scalar is used to convert the raw ’load’ values into more meaningful physical units.

Pedal as Load

If Fuel Map Pedal is On, then a correction, Boost Correction from the Boost Correct table is used to correct for the change in air pressure entering the engine.

This can result in a more responsive Pedal.

Note the Fuel Pedal map is used instead of Fuel map as the base fuelling in this case.

MAF Sensor

Overview

The Mass Air Flow (MAF) sensor measures the mass of air entering the engine. This may optionally be used to calculate the amount of fuel required to maintain the desired air/fuel ratio.

The MAF sensor is typically a hot wire or hot film sensor, which heats a wire or film to a constant temperature and measures the cooling effect of the air flow. The cooling effect is proportional to the mass of air flowing past the sensor.

The voltage output of the MAF sensor is often non-linear, so the ECU may apply a calibration curve to convert the raw voltage into a more useful linearized form.

MAF Sensor Options

Option	Description
MAF	Use MAF as the “Engine Load” measurement?
MAP	Set to 0 if using MAF for Engine Load.
Load source	Do not set if using MAF for Engine Load.
MAF source	Select an input channel to use for MAF. This could be an Analogue input or another source such as CAN bus.
MAF source Bigend	Swaps the bytes from the 16bit MAF source. This may be required if the source is from a little-endian (Intel) 16bit CAN signal.
MAF Raw	Raw MAF sensor reading as obtained from the MAF source.
MAF no Speed comp	If ON, the MAF sensor reading is not compensated for engine speed. Otherwise, the MAF sensor reading is multiplied by the inverse engine speed and divided down.
MAF no X16	If ON, the MAF sensor reading is not multiplied by 16, following speed compensation. This option does nothing if MAF no Speed comp is ON.
MAF Sensor	MAF Sensor Table to convert raw MAF sensor voltage into a linearized form.
MAF Cal	Number of internal teeth over which to average the MAF sensor readings when running. Typically this would be set to 1, 2 or 3 revolutions; the actual value to set here would depend upon the number of internal teeth per revolution which should be configured in the Wheel Teeth option.
MAF min	Minimum MAF sensor reading, below which an error condition is indicated.
MAF max	Maximum MAF sensor reading, above which an error condition is indicated.
MAF Linear	Linearized MAF reading, scaled using MAF (Load) Scalar.
MAF Linear Scaled	Linearized MAF reading, scaled using MAF Scalar.
MAF as Load	Compensated MAF reading, scaled using MAF (Load) Scalar.
MAF as Load Scaled	Compensated MAF reading, scaled using MAF Scalar.
Error MAF	Indicates an error condition with the MAF sensor.

Flowchart

flowchart TD
    MAFMIN@{ shape: diamond, label: "< MAF Min"}

    MAFMAX@{ shape: diamond, label: "> MAF Max"}
    MAFNSPD@{ shape: diamond, label: "MAF no Speed comp"}
    NOMAFMUL@{ shape: diamond, label: "MAF no X16"}

    MAFRAW["MAF Raw"]

    MAF_Source(["MAF source"])-- RUNNING? -->MAFSMP(["MAF samples"])
    MAFSMP-->MAFAVG["Average"]-->MAFRAW
    MAFCAL(["MAF Cal [teeth]"])--"Window Size"-->MAFAVG
    MAF_Source--"NOT RUNNING"-->MAFRAW

    MAFRAW-->MAFMIN
    MAFMIN-- Y -->ERROR_MAF(["Error MAF"])
    MAFMIN-- N -->MAFMAX

    MAFMAX-- Y -->ERROR_MAF(["Error MAF"])
    MAFMAX-- N -->MAFTBLW["MAF Sensor Table"]
    SPEEDN(["− Engine Speed"])
    MAFTBLW-->MAFLIN(["MAF Linear [MAF Load Units]"])
    MAFLIN-->MAFLINSCALED(["MAF Linear Scaled [MAF Units]"])
    

    MAFLIN-->MAFNSPD
    MAFNSPD-- N -->SPEEDMUL["×"]
    MAFNSPD-- Y -->MAFLOAD
    SPEEDN-->SPEEDMUL

    SPEEDMUL-->NOMAFMUL

    NOMAFMUL-- N -->MUL16["×16"]
    NOMAFMUL-- Y -->MAFLOAD
    MUL16--> Overflow -->ERROR_MAF
    MUL16-->MAFLOAD

    MAFLOAD(["MAF as Load [MAF (Load)]"])

    MAFLOAD-- "MAF AND NOT MAP AND NOT "Load Source"" -->LOAD(["Engine Load [Load]"])
    MAFLOAD-->MAFLOAD_SCALED(["MAF as Load Scaled [MAF Units]"])

MAP Sensor

Overview

MAP sensors measure the pressure of air entering an engine (Manifold Absolute Pressure). This information may be used by the ECU to calculate the amount of fuel required for combustion.

There are typically two MAP sensor inputs on the ECU, with the two sensors being used for redundancy and error checking.

The voltage output of the MAP sensor is typically linear with pressure, and the ECU can be configured to convert this voltage into a pressure reading in kPa.

The MAP sensor can optionally be used as a measure of Engine Load, in which case the ECU will convert the pressure reading into a load value. This load value is used as an axis input for many of the ECU’s calibration tables such as the Fuel map or the Ignition map.

Calibration

Option / Channel	Description
MAP	Use MAP as the “Engine Load” measurement?
MAF	Set to 0 if using MAP for Engine Load.
Load source	Do not set if using MAP for Engine Load.
MAP Source	The source of the MAP sensor data. This is an analog input number.
MAP2 Source	The source of the 2nd MAP sensor data. This is an analog input number. If using a single MAP sensor, MAP2 Source should be set to the same value as MAP Source
MAP Cal	Number of internal teeth over which to average the MAP sensor readings when running. Typically this would be set to 1, 2 or 3 revolutions; the actual value to set here would depend upon the number of internal teeth per revolution which should be configured in the Wheel Teeth option.
MAP1 samples	When running this table is filled with the samples used for averaging MAP1.
MAP2 samples	When running this table is filled with the samples used for averaging MAP2.
MAP raw Invert	Inverts the MAP sensor reading, useful for some sensors that output a voltage that decreases with pressure. This same setting applies to both MAP sensor inputs.
MAP1 raw	Result of averaging / inverting the MAP sensor voltage readings. This value can be monitored to verify the MAP sensor input configuration and that the analogue input is reading the MAP sensor correctly.
MAP2 raw	Result of averaging / inverting the second MAP sensor voltage readings. This value can be monitored to verify the MAP sensor input configuration and that the analogue input is reading the MAP sensor correctly.
MAP Min Error	The minimum valid voltage for the MAP sensor. If MAP raw reads below this value, an error will be triggered Error MAP. If MAP2 raw reads below this value, an error will be triggered Error MAP2.
MAP Max Error	The maximum valid voltage for the MAP sensor. If MAP raw reads above this value, an error will be triggered Error MAP. If MAP2 raw reads above this value, an error will be triggered Error MAP2.
MAP ref low Volts	The voltage output of the MAP sensor at a low pressure reference value MAP ref low Pressure.
MAP ref low Pressure	The physical pressure reading from the MAP sensor when the voltage reading from the analogue input reads MAP ref low Volts.
MAP ref high Volts	The voltage output of the MAP sensor at a high pressure reference value MAP ref high Pressure.
MAP ref high Pressure	The physical pressure reading from the MAP sensor when the voltage reading from the analogue input reads MAP ref high Volts.
MAP Pressure Max	If non-zero, this overrides the calculated MAP for Load Max for re-scaling MAP.
MAPM	The MAP sensor calibration multiplier, derived from the reference low and high pressure and voltage values.
MAPC	The MAP sensor calibration constant, derived from the reference low and high pressure and voltage values.
MAP for Load Max	Indicates the maximum pressure that the MAP sensor can read. This value is used to scale the MAP sensor readings to a load value.
MAP for Load Scalar	Alias of MAP for Load Max
MAP1 abs	The absolute value of the MAP sensor reading, in kPa.
MAP1 abs FP	The absolute value of the MAP sensor reading, scaled using Fuel Pressure Scalar.
MAP2 abs	The absolute value of the second MAP sensor reading, in kPa.
MAP2 abs FP	The absolute value of the second MAP sensor reading, scaled using Fuel Pressure Scalar.
MAP abs Peak	Maximum of MAP1 abs or MAP2 abs, in kPa.
MAP abs Peak FP	Maximum of MAP1 abs or MAP2 abs, scaled using Fuel Pressure Scalar.
MAP1 as Load	MAP abs is rescaled by the ECU to make more use of the full-scale range. Scaled to physical units using Load Scalar.
MAP2 as Load	MAP2 abs is rescaled by the ECU to make more use of the full-scale range. Scaled to physical units using Load Scalar.
MAP1-MAP2	The difference between MAP1 as Load and MAP2 as Load.
MAP1+MAP2/2	The average of MAP1 as Load and MAP2 as Load.
MAP as Load	The average of MAP1 as Load and MAP2 as Load, unless an error is detected (e.g. out of range voltage) in either input, in which case the valid input value is used where possible.
Engine Load	If the ECU is configured to use MAP as the measurement of Engine Load, this channel will show the value of MAP as Load. This value is scaled to physical units using Load Scalar, as with MAP as Load.
Error MAP	Error flag for MAP sensor 1. Set if the voltage reading is outside the range defined by MAP Min Error and MAP Max Error.
Error MAP2	Error flag for MAP sensor 2. Set if the voltage reading is outside the range defined by MAP Min Error and MAP Max Error.
Barometer	The barometric pressure reading, in kPa.
Boost1 gauge	The difference between MAP1 abs and Barometer, in kPa.

MAP as Load Scaling

The MAP1 abs value is rescaled to make full use of the range. This may therefore require adjustment to the Load Scalar to arrive at correct pressure values for MAP as Load and Engine Load.

Be aware that if the MAP sensor is not being used as a measure of Engine Load then the Load Scalar could be in use by something else. For example, if Load source is being used for Engine Load then the Load scalar may be responsible for rescaling the data selected by Load source so that Engine Load is in the correct units.

Flowchart

flowchart TD
    MAPMINER@{ shape: diamond, label: "< MAP Min Error"}

    MAPMAXER@{ shape: diamond, label: "> MAP Max Error"}
    MLDMAX_D@{ shape: diamond, label: "> MAP for Load max"}

    BARSCLD(["Barometer"])
    MAP1_abs(["MAP1 abs"])

    MAP_Source(["MAP Source (A2D)"])-- RUNNING? -->MAP1SMP(["MAP1  samples"])
    MAP1SMP-->MAP1AVG["Average"]-->MAP_raw_Invert
    MAPCAL(["MAP Cal [teeth]"])--"Window Size"-->MAP1AVG
    MAP_Source--"NOT RUNNING"-->MAP_raw_Invert["MAP raw Invert?"]
    MAP_raw_Invert-->MAPRAW1(["MAP1 raw [V]"])
    MAPRAW1-->MAPMINER
    MAPMINER-- Y -->ERROR_MAP(["Error MAP"])
    MAPMINER-- Y -->MAP_ZERO["0"]-->MAP1_abs(["MAP1 abs"])

    MAPMINER-- N -->MAPMAXER

    MAPMAXER-- Y -->ERROR_MAP(["Error MAP"])
    MAPMAXER-- Y -->MAP_FULL["MAX"]-->MAP1_abs(["MAP1 abs"])
    MAPMAXER-- N -->MAP1M["×"]
    MAPM-->MAP1M
    MAP1M-->MAP1C["+"]
    MAPC-->MAP1C
    MAP1C-->MAP1_abs

    MAP1M_SRC["(MAP ref high Pressure − MAP ref low Pressure) / (MAP ref high Volts − MAP ref low Volts)"]
    MAP1M_SRC-->MAPM(["MAPM"])

    MAP_Ref_low_v["MAP ref low Volts"]-->MAPC_M["×"]
    MAPM-->MAPC_M

    MAP_Ref_low_p["MAP ref low Pressure"]-->MAPC_C["−"]
    MAPC_M-->MAPC_C
    MAPC_C-->MAPC(["MAPC"])

    MAPC-->MLDMAX_ADD["+"]
    MAPM-->MLDMAX_ADD["+"]
    MLDMAX_ADD-->MLDMAX(["MAP for Load Max [kPa]"])
    MLDMAX_ADD-->MLDS(["MAP for Load Scalar"])

    MLDMAX-->MLDMAX_D
    MLDMAX-->MAP1_abs_DIV

    BARSCLD-->MAP1_abs_sub
    MAP1_abs-->MAP1_abs_sub["−"]

    MAP1_abs_sub-->BSTGAGE1["Boost1 gauge"]

    MAP1_abs-->MLDMAX_D
    MLDMAX_D-- Y -->MAP1_abs_FULL["MAX"]-->MAPLOAD1(["MAP1 as Load [Load]"])
    MLDMAX_D-- N -->MAP1_abs_DIV["/ MAP for Load max"]-->MAPLOAD1(["MAP1 as Load [Load]"])

    MAPLOAD1-->MAPLOAD1_MINUS_2
    MAPLOAD2(["MAP2 as Load [Load]"])-->MAPLOAD1_MINUS_2

    MAPLOAD1_MINUS_2["−"]-->MAPLDIFF(["MAP1-MAP2 [Load]"])

    MAPLOAD1-->MAPLOAD1_AVG_2
    MAPLOAD2-->MAPLOAD1_AVG_2
    MAPLOAD1_AVG_2["Average OR Select"]-->MAPLDAV(["MAP1+MAP2/2 [Load]"])
    MAPLOAD1_AVG_2-->MAPLOAD(["MAP as Load [Load]"])

    MAPLOAD-- "MAP AND NOT MAF AND NOT "Load Source"" -->LOAD(["Engine Load [Load]"])