[Gmecm] Back to square one

[davesnothereman at netscape.net]

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

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