Changing 165 / Nother Q

[Romans, Mark]

Dave:  I have a ported maf on my Vet.  I have had to adjust the calibration
only in the smallest calibration table.  BL has stayed close to 128 at all
other areas so I am assuming that the calibration has not been thrown off.
The problem is once again in that the software doesn't read above 255
grams/sec.
I have thought about, but taken no action on looking at the Porsche 928
bosch maf sensor.  It is supposed to have a  larger ID and flow more air. I
would attempt to adjust the injector constants to make fuel match up with
air flow.  I would lose some accuracy, but it would be no different than
what the 730 does.
Mark

----- Original Message -----
From: "Dave Zug" <dzug at delanet.com>
To: <gmecm at diy-efi.org>
Sent: Saturday, June 17, 2000 1:07 AM
Subject: Re: Changing 165 / Nother Q


400000000000000000 / 256 = 156250000000000 (close)  G/S per single unit of
resolution on the sensor....

Your point is understood,  but I'd use MAP for the jet engine ;-)

converting to 16 bit would be useful only if the sensor range was also
raised.  If you turn an 8 bit value into a 16 bit, it just gives you the
ability to see the sensor value as more tiny-er steps... not higher values.
you would have to change the sensor range at the same time to be able to
read more air.  (9 bits will get you to 512 steps,  BTW).  sorry this may be
out-of-place rambling, I don't understand how this is done very easily. IN
the code, the A2D would see a maxxed input, translate to FFh, and that may
trigger some creative code to say "go to the high table" but the input still
will be pegged.  you'd almost have to electronically reduce (re-scale) the
voltage input from the MAF to the ECM, then allow the internal 9-bit (16
bit) value to read 255 when the voltage level was at 4v or something,  then
have the internal 9-bit read 320 at 5v... a second "high" table would have
entries that were up to (320 minus 255), and would be in use only when the
"high flow" bit (9th) was lit.

oooh my brain, the POOR '165  ;-)  Please, as always... someone add /
correct me so I don't confuse others browsing the archives.

I have used the RPM based fuel tweak to compensate for what the MAF can't
see.  Its a trial and error method, but I got it to work out when I had the
Supercharger on.  I started reeeal rich, and used o2 to make sure I wasn't
lean, but I should have backed it up with an EGT.

Makes sense to me that if you can increase the size of the MAF (not saying
anything new here) that the readout for a given flow rate will decrease
exactly proportionally with the increase in orifice area.  the big job is to
go thru EVERY calculated value (on chip) and every comparison made to those
values, and adjust them accordingly.  i.e.  trip into PE mode at a MAF value
of 40(d) insted of 55(d) because now 40 represents 55 g/s and 255 represents
320 g/s (or whatever math...)

To MY Question:

Has anyone scientifically measured the effect on readings between an
unported, stock, screened MAF and a ported (no sink) and un-screened MAF? I
figgered roughly the percentage of area opened up, and a little tweak for
the reduction in air turbulance and went with that to re-calibrate the MAF
tables. I figgered a shop vac and a y-pipe and a volts meter would give a
ratio as well.  anyone done it?  share?  of coarse the voltage reading will
be lower for the gutted MAF,  but it would be cool to have a graph of each
at all flow levels ;-))



----- Original Message -----
From: Mike Rolica <mrolica at meridian-mag.com>
To: <gmecm at diy-efi.org>
Sent: Thursday, June 15, 2000 1:05 PM
Subject: RE: Changing 165 fuel delivery was "General tuning question - fuel
economy"


Argggg.. yes it can pull in 40000000000000000000times more air  but as long
as you are in the range of the maf... ie below it's max sensing cap ie 254
g/s  then the maf is fine.

Senario 2.. lets say at 2500rpm  and ½ throttle, and you are pulling 255g/s
then the ecm thinks this is max air it can get....so it cant regognize and
more air.... That is why I would like to create a patch to use either 2
tables or go 16 bit!!!!


<BIGSNIP>

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