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

[Mike Rolica]

Mike Rolica
Plant A,
Magnesium Products Division
Strathroy

(519)-245-4040  Ext. 265


		-----Original Message-----
		From:	Bruce Plecan [SMTP:nacelp at bright.net]
		Sent:	Thursday, June 15, 2000 3:56 PM
		To:	gmecm at diy-efi.org
		Subject:	Re: Changing 165 fuel delivery was "General
tuning question -fuel economy"



		> Ok  FROM WHAT I'VE FOUND  mass air is a direct measurement
of the amount
		of
		> air going into the engine.

		Nope, it's a calculation, Just the electronics to it are
self contained
		rather then a MAPs where it's done in the ecm.
		It references MAF to a voltage drop,  this voltage drop
assumes the humidity
		is a constant.  Also, assumes the O2 percentage is a
constant.  Both are
		errors, if it was accurate there would be no need for
feedback.
		Just cause something is called something don't make it so.
Look at the
		knock detector, it's not a knock detector, it's a noise
detector tuned for a
		common freq. of knock.
		  If they were as they claimed life would be a piece of cake
for tuning.
		If the MAF and injector calibrations were right, then you
would never have
		to change any of those variables.  All you'd ever need to do
is pick the
		right MAF for the HP level of the car, and it's matching
injectors, and ecm.
		Guess what don't work out like that for the gm's.



		Yes BUT those errors are fairly small.. the blm is ito make
up for humidity and crap... what I'm saying is that if an engine's flow
charachteristics are changed.. maf will still tell you the amount of air
going in with the same error that it did before the mods... with map,
eveything goes out of whach...... map is based on pressure drop... plain and
simple.. you said yourself that vacume or pressure changes in a modified
engine..

		snip

		> 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....

		Assuming the MAF theory was accurate, and since it's not
then tinkering is
		needed.  Changing Air Filter Types can effect the MAF since
the turbulence
		of the air going across the wire changes.

		> For map since the ve represents the cd of the motor...
different motors
		will
		> have differing cd's

		MAP has to be tuned to a specific engine, yes.  cd?.   
		 

		CD coefficient of discharge.


		> 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...

		Have you hooked a scope to see if the MAFs output is capable
of reading a
		high gms/sec?.  If you have what did the numbers do, if you
don't mind
		sharing.

		Tested the maf on a flow bench hooked up to a 52mm tb and
plenum....

		Got maf to put out fairly linear from 0 to 10v.... think 10
volts was some where aroun 600g/s...I'll have to check.
		So yes it is capeable..

		> 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..

		Kinda a big jump to get there thou.  The MAF is always
reading behind the
		actual flow across it other then steady state.  The system
is little better
		then Alpha-N in my book.  It seems to be more like a Apha-N
that fine tunes
		cruise mode with the MAF.  That's why they can run so good
for diagnostics
		with no MAF signal.  The MAF is useless in sudden
transistions.  MAP is dam
		near real time the errors is in the diam lenght of the
sensor line.

		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....

		as possible.   As Possible varies the second you get away
from the oem
		ducting.

		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....

		Motors by application.  Vehicle weight gearing under hood
air flow, all play
		a part.
		Grumpy




		Agreed.....

		> Mike Rolica


	
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