[Gmecm] Back to square one

[Robin Handley]

This got me wondering; why did GM build in the ability to switch between 1
BAR and 2 BAR MAP sensors in $58 when they didn't actually produce a vehicle
which used it? :-)

R

----- Original Message -----
From: <davesnothereman at netscape.net>
To: <gmecm at diy-efi.org>
Sent: 14 May 2006 20:18
Subject: Re: [Gmecm] Back to square one


> The pressure <-> voltage relationship for the 1 and 2 BAR sensors are
> not exactly linear.  This becomes even more apparent for the 3 BAR
> saneor.  The lower the pressure, the closer the voltage between the two
> sensors.  And really, they both have to represent about 20 kPa as
> something close to 1V.  I believe there is a PV chart for the 2 BAR
> sensor accessible from the gmecm home page.  Promgrammer's scaling is
> most likely correct.
>
> The only 1 BAR calibration I'm aware of for the 7749 is used with the
> Quad 4 engine.  That's more better suited to high rpm use.  It's also
> long overdue to be hacked / disassembled.
>
> Used sensors vary in price depending on where you go shopping.  Send me
> an email off list.
>
> Zaphod
>
>
> -----Original Message-----
> From: Robin Handley <Robin at FuryWorld.fsnet.co.uk>
> To: gmecm at diy-efi.org
> Sent: Sun, 14 May 2006 17:44:34 +0100
> Subject: Re: [Gmecm] Back to square one
>
>   > What I can say with certainty is that flipping the bit to 1 BAR and
> > connecting to a 1 BAR sensor produced poor idle and driveability in my
> > car.  I had no desire to chase the reason, I simply switched to a 2
> BAR
> > sensor.  I valued the time spent more than the potential for
> education.
>
> I've been comparing what values PROMgrammer shows for pressures (kPa),
> for
> the same Sunbird.bin, but when the MAP sensor range flag is changed:
>
> Some calibration values are approximately halved.
> Some are identical.
> Some are approximately the same.
>
> So, PROMgrammer seems to be applying different scale factors/formulae,
> to
> convert the raw stored value into kPa, for different calibration values.
> Whether it is doing this when appropriate I just don't know. I had been
> hoping that the GM programmers had been sufficiently clever so that raw
> values (stored in the .BIN) would be appropriate no matter what sensor
> range
> is chosen, but I'm beginning to wonder if this was wishful thinking. If
> life
> isn't that simple (and I expect it isn't), then I reckon I've
> potentially
> got a yucky job on my hands to try and work out what new values should
> be
> used. This could be made all the more difficult if PROMgrammer's
> scalings
> aren't right - as I could be putting in a perfectly sensible value of
> kPA,
> which is then scaled to something stupid. :-( I'd be very grateful if
> somebody could comment here. :-)
>
> Dependent on what the expert response is, the option of buying a 2 BAR
> MAP
> sensor is looking more attractive. Anybody know what a scrap one goes
> for?
> Are they easy to come by?
>
> The last option that I can think of is to find a set of calibration
> values
> for $58 from a NA car. Anybody know if one of these exists? Were all
> Sys/Tys
> Turboed?
>
> Robin