Changing 165 fuel delivery was "General tuning question -fuel economy"

[Mike Rolica]

Ok  FROM WHAT I'VE FOUND  mass air is a direct measurement of the amount of
air going into the engine.  The maf vr rpm is just a calibration of the
maf.. as you would calibrate a mass flow meter or any other process
instrumentation.....
Map, is using a differential pressure to come up with an amount of air.. ie
it is similar to measuring flow by measuring the pressure drop across an
orifice plate.. the engine is the orifice plate in the pipe.. get it??
Now with an orifice plate, you need some constant or value that is
particular to it to convert the pressure drop to flow rate.. for an orifice
plate it is the coefficient of discharge..
The ve tables represent the coefficient of dischare of the engine ...in
simplistic term(so don't flame me... I'm not about to go into the theory!!!)
>From the pressure drop indicated from the map sensor the ve tables relate
that pressure drop to a flow rate...except for an engine the cd is always
changing....

So for a maf application.. the tables theoretically should not change for
any motor you put the maf sensor on.. as long as that engine is within the
span of the maf..   once the signal from the maf is calibrated to a
flowrate... it should not change on any motor....
For map since the ve represents the cd of the motor... different motors will
have differing cd's


As disscused before on this list.. the maf runs into trouble with high perf
engines because the engine pull more air than the ul of the maf.... Or the
range of the maf is to narrow....if their was a maf that would measure a
higher amount of flow it would be ideal.. cept you would then have to edit
the tables to reflect the output of the maf to actual flow rate...  another
option that was discussed was to somehow patch the code so the maf range was
16bit instead of 8.. hence doubling the range..... I'm working on that right
now by adding a table like the ve on the 730...maf high and maf low....where
255=255g/s and max on maf high would be 255 or 510g/sec.. so that one the
maf sig reached 250 or so it would switch to maf high.. (there would also
have to be compensaion for hysterisis  ie goto maf high at 250g/s  then go
to maf low at  30g/s.. there is also some other avenues I'm looking at...


	Now that we have the air covered, we have to let the ecm know how
much fuel to mix with that air.... Lets say the maf is calibrated.. then it
has to know the fuel flow  it gets this from the injector size. From the afr
goal  ie 14.7:1 it now knows how long to keep the injector open in order to
get that ratio... some people fiddle with the injector size to fool the
ecm.. I tend to like to calibrate the maf.....so the maf tables are
right....then put the actual g/s of fuel my injectors put out  (at their
pressure) and change the a/f ratio till it is where I want it.... Then iu
tune the spark  back to afr... ect..  the maf tables can also be changed if
you fingd a lean spot in your range .. but if calibrated right this should
no happen... also the pe functions should be looked at in order to get max
performance out of the motor..cause diff motors have differing likings for
the amount of fuel you need when you mash the gas....  

There is also tons of other stuff but this is getting prety long..
Mike Rolica
Plant A,
Magnesium Products Division
Strathroy

(519)-245-4040  Ext. 265


		-----Original Message-----
		From:	Rick Lindstedt [SMTP:rick at mafb.org]
		Sent:	Thursday, June 15, 2000 12:44 PM
		To:	gmecm at diy-efi.org
		Subject:	Re: Changing 165 fuel delivery was "General
tuning question -fuel economy"

		Marteney, Steven J. wrote:
		>I haven't got my copy of tunercat yet, but it's coming, or
the rather the
		>check is going.  In the meantime, to increase fuel across
the board, TC has
		>two settings for injector flow rate, single and double
fire.  Is that what I
		>can use for this?  I remember a couple of months ago there
was a lot of

		I dont know about that one..

		>hand-waving about single-fire and double-fire and what the
difference was.
		>Hate to bring it up, but was there a clear answer that came
out of that?


		No definete answer came ...I was the one that brung it up in
the first 
		place.. =/ I am still wondering if there any real
gains/losses from 
		switching from one to the other or if there are any...

		>Also, in the 165, is there an equivalent to the VE tables
as in the speed
		>density stuff?  I didn't see anything in CATS function list
other than "Mass
		>Air Flow vs. RPM, (Diag)" and the injector flow rate
constants.

		That all I saw when I looked into the CATS...  I use GMEPro
tho..

		Rick
		  

	
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