Barometric pressure

[Jason Haines]

Which above reference GM? You don't mean the 1994 LT1 Camaro that was
originally asked about do you? As far as I know, the LT1 PCM as used on the
Camaro/Firebird/Corvette/Impala has a MAP and a MAF input but no barometric
pressure sensor (onboard the PCM or offboard as an input) and the LT1 ECM
has MAP only (1992-1993 applications).

Jason

>
> There are several strategies.
> Some take a glance at startup, then others at 3/4 throttle, do a review of
> it
> The earlier ones use a full time baro sensor.
> (the above, reference GM)
> Bruce
>
>

>
> > I never knew the Baro value changed...until next key on. One reason is
> that
> > you can start an EFI down here, drive to Banff--and it's running on the
> rich
> > side till you stop for gas <G>... suddenly, it's fixed. The 3000 ft
> > elevation change isn't updated till next key on cycle. If they're using
a
> > WOT run for an update, I dunno--IMO it's not the whizziest idea in the
> park.
> >
> > Lyndon.
> > ----- Original Message -----
> > From: "Jason Haines" <jhaines at lingenfelter.com>
> > To: <diy_efi at diy-efi.org>
> > Sent: Thursday, September 13, 2001 11:08 AM
> > Subject: Re: Barometric pressure
> >
> >
> > > On the newer GM vehicles, (such as the 1994 application originally
asked
> > > about) the MAP sensor is used to determine the barometric pressure. In
> > > addition to setting the barometer to the MAP reading at key up, the
MAP
> > > readings are also compared to the stored barometer reading under
> different
> > > conditions (WOT being one of them) and changed based on the expected
> > > pressure drop in the system at different RPM levels, throttle
positions
> > and
> > > air flows (in MAF based systems). Different vehicles, ECMs etc. have
> > > different levels of complexity of this model.  It is my understanding
> that
> > > one of the reasons for doing this form of barometric pressure
updating,
> in
> > > addition to whatever issues the OE may have, is to comply with EPA and
> > CARB
> > > requirements for altitude compensation (manufacturers are no longer
> > allowed
> > > to have separate high altitude calibrations).
> > >
> > > Some appilications do use a separate barometric pressure sensor but
this
> > is
> > > rare (I only know of one GM application).
> > >
> > > The above information applies to GM vehicles but should be true for
many
> > > other applications. They all want to save money on sensors so they try
> to
> > > reduce the content on the ECM and in the vehicle (plus, less parts
means
> > > less parts to go bad).
> > >
> > > Just my $0.02
> > >
> > > Jason
> > >
> > >
> > > > As far as I know--it's only a snapshot at key on.
> > > > I don't know how it'd do it at WOT...if exhaust was
> > > > partially plugged, it'd really wonk the settings.
> > > >
> > > > Lyndon.
> > > > ----- Original Message -----
> > > > From: "terryk" <terryk at foothill.net>
> > > > To: <diy_efi at diy-efi.org>
> > > > Sent: Wednesday, September 12, 2001 7:00 PM
> > > > Subject: Re: Barometric pressure
> > > >
> > > >
> > > > > Correct me if I'm wrong, but doesn't some early code measure it at
> > WOT?
> > > > >
> > > > > TK
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Programmer" <nwester at eidnet.org>
> > > > > To: <diy_efi at diy-efi.org>
> > > > > Sent: Wednesday, September 12, 2001 5:17 PM
> > > > > Subject: Re: Barometric pressure
> > > > >
> > > > >
> > > > > > The MAP sensor (at key on).
> > > > > >
> > > > > > Lyndon.
> > > > > > ----- Original Message -----
> > > > > > From: "bob r johnson" <bobj_johnson at juno.com>
> > > > > > To: <diy_efi at diy-efi.org>
> > > > > > Sent: Wednesday, September 12, 2001 7:03 PM
> > > > > > Subject: Barometric pressure
> > > > > >
> > > > > >
> > > > > > > Could someone tell me, on a 94 Z28, what sensor measures
> > barometric
> > > > > > > pressure?
> > > > > > > Thanks,


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