Barometric pressure

[Programmer]

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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