Barometric Pressure Compensation
The current Barometric pressure correction table is a four-by-four fuel
multiplier indexed by barometric pressure and RPM. Its default cells are all
1.0, so the table does nothing until it is calibrated. The TunerStudio menu is
displayed only when the selected fuel model is Speed Density, but that is a
visibility condition, not a runtime gate. The running-fuel correction stack
includes the computed baroCorrection value globally. Alpha-N also has separate
alphaNBaroCompensation and alphaNBaroReferencePressure controls.
baroCorrTable, baroCorrPressureBins, and baroCorrRpmBins define the lookup.
The resulting baroCorrection is consumed in the running-fuel correction stack
after the base air mass is calculated. Calibrate it only from measured behavior
for the installed intake and operating range; changing the axis breakpoints
changes what each row means.
Failure behavior is specific. If no barometric-pressure sensor is registered,
getBaroCorrection() returns 1. If a sensor is registered but has no valid
value, the lookup uses 101.325 kPa as its pressure fallback. A lookup result
that is NaN or below 0.01 produces the Invalid baro correction warning
and returns 1. That warning itself emits
OBD_Barometric_Press_Circ_Range_Perf; there is no separate sensor-checker
diagnostic for this path.
For a MAP-derived start-up value, useFixedBaroCorrFromMap can seed the
barometric-pressure sensor from MapSlow. A missing MAP value defaults to
101.325 kPa, so an absent sample can seed standard atmospheric pressure. The
result is accepted only from 60 to 110 kPa; otherwise the fixed value is
disabled. The decoder has no RPM gate, so it cannot prove the engine is stopped:
the operator must ensure that condition before initialization or a re-read.
Use a dedicated barometric sensor when continuous ambient-pressure change
matters.
During diagnostics, compare the baroCorrection gauge with barometric pressure,
RPM, MAP, and the live correction cursor. Confirm the barometric sensor is
registered before interpreting unity. If unity is reported, check whether the
Invalid baro correction lookup warning was logged. That warning itself emits
OBD_Barometric_Press_Circ_Range_Perf when the lookup result is NaN or below
0.01, rather than through a separate sensor-checker diagnostic. See
Load Sources and
Alpha-N for the model-specific paths.