[Shotimes] BARO sensor

[Kevin & Cheryl Airth]

Thanks Adam!
 So the DPFE does NOT tell the PCM what the BP/MAP is? But BP is calculated
or inferred from the other sensors? I had it in my head that somehow the
DPFE fed a BP/MAP reading to the PCM.

 Now this makes me ask: If the BP can be inferred from other sensors, why
would a cheapskate like Ford spend the money to install a separate BP
sensor? Also the SHO does NOT have a MAP sensor (and this is required) so
the inferred method seems to be missing something for our SHO's? The
equation below does not use a MAP input so maybe the MAP is not needed as an
input at all?
.
.



> >> Well, We get to mess with the DPFE which is MUCH more failure prone and
> complicated than the BAP setup!!! <<
>
> No argument there.  :)
>
> >> Which brings up a bit of trivia that I have not figured out. Maybe
someone
> with a California MTX can help? If the car is a MTX with EGR does it have
both
> a DPFE and a BAP sensor? Or does it lose the BAP and use the DPFE like all
the
> ATX cars do? <<
>
> While I am no wiser than Ian regarding which CA MTX cars may (or may not)
have
> received a BARO sensor, I can satisfy the question regarding how BARO
readings
> are inferred on non-BAP-equipped cars (such as the Gen 2 ATX).  To do
this, I
> refer you to the factory EEC strategy documentation:
>
> --
> INFERRED BAROMETRIC PRESSURE STRATEGY
>
> BACKGROUND:
>
> Earlier EEC systems used two pressure sensors (manifold absolute and
> barometric absolute pressure) to provide full altitude capability.  Since
both
> sensors perform the same function (i.e. measure pressure), elimination of
one
> sensor, via time sharing or software inference was considered a
significant
> system cost reduction.  Since MAP is a primary  input for both spark and
fuel
> control and BAP is a secondary modifier, elimination of BAP sensor
resulted in
> cost reduction.
>
> In the Inferred Barometric Pressure strategy, the BAP sensor is replaced
by a
> software algorithm which uses available inputs (i.e. MAP, RPM, Throttle
> Position, ECT) to infer the Barometric Pressure.  The EEC-IV  Barometric
> Pressure (BP) is saved in Keep Alive Memory (KAM) to bridge the power-down
to
> power-up sequence.
>
> FUNCTIONAL DESCRIPTION:
>
> The barometric pressure is inferred from other sensor inputs.  With air
meter
> equipped engines redundant sensor and actuator information exists which
allows
> for the inference of barometric pressure.  The basic equation is:
>
>                            29.92 * air mass from airmeter
>  Inferred BP = --------------------------------------------------------
>                sqrt(560/(ACT+460)) * inferred air mass (29.92,100 ACT)
>
> The model implied by the inferred BP equation is that the inferred air
mass is
> really an air volume flow calculation, converted to mass units at the
standard
> temperature and pressure.  The air meter is a true air mass measurement
> device.  Thus, deviations in mass from the inferred calculation are
attributed
> first to inlet temperature, which is measured and then to a drop in inlet
> pressure, which is the inferred BP.
>
> In the EEC the air mass flows are converted to LOAD by the formula:
>
>  load = air mass / (N * ENGCYL * SARCHG).
>
> The inferred BP formula in EEC terms is thus:
>
>         29.92 * LOAD from airmeter
>  IBAP = --------------------------
>            FN059(ACT) * TOTLDST
>
> N is engine speed in RPM.
>
> ENGCYL is the umber of PIPs per revolution (cylinder number/2).
>
> SARCHG is the standard air charge for a single cylinder.
>
> TOTLDST is the inferred air mass RAM value.  It is the sum of the flow
through
> the throttle body.
>
> TPLDST and the flow through the air bypass valve, BYLDST.  TPLDST is a
table
> lookup versus N and TP_REL.
>
> BYLDST is the load equivalent of BYMAST, the air mass flow through the air
> bypass valve.
>
> BYMAST is calculated from a table lookup of air bypass duty cycle.
>
> ISCDTY and a calculation of percent load, PCT_LOAD.
>
> For calibration purposes, the calculated inferred value of barometric
> pressure, can be fixed by using the calibrateable value BAPFMM.
> --
>
> Hopefully that didn't bore too many people.  ;)
>
> Adam