[Gmecm] Re: MAF specs and MAP replacement.

[Steve Ravet]

The end goal of EFI is to inject the correct amount of fuel for the mass
of air that is passing through the engine, to produce the desired
air-fuel ratio.  So knowing the mass of air passing through the engine
is the crucial bit of information.
 
MAF measures mass directly.  If you don't have MAF then you have to
calculate mass.  Look up the ideal gas law, PV=nRT.
 
P=pressure
V=volume
n=mass
T=temperature
R=constant to make units work out correctly.
 
MAP gives you pressure.  Volume is calculated from RPM.  T comes from
the inlet air temp sensor, or is just a constant.  This calculation is
generally done beforehand and stored in the form of a volumetric
efficiency table that is indexed via MAP and RPM.
 
So your box will have to take MAP and RPM as a minimum, and will have to
have some constants related to the engine in there also.  What's your
application?  I think most MAF systems fall back on MAP in the case of a
defective MAF sensor, you can probably "convert" to MAP by simply
unplugging the MAF.
 
--steve


________________________________

	From: gmecm-bounces at diy-efi.org
[mailto:gmecm-bounces at diy-efi.org] On Behalf Of Michael Stephens
	Sent: Thursday, May 19, 2005 7:13 PM
	To: gmecm at diy-efi.org
	Subject: [Gmecm] Re: MAF specs and MAP replacement.
	
	
	Arent the wiring harnesses incombpatable.   I thought the MAF
did alot of other things the MAP did not.   Is it really just as easy as
rewriting a chip?
	
	
	On 5/19/05, Michael Stephens <89iroc at gmail.com> wrote: 

		Hi all,
		I might have asked this question before but I cant
remember.   I am starting to learn about microproccessors and I want to
build a device that scraps the MAF and uses MAP instead.  I know
generally you have to change the whole wireing harness but I would like
to use MAP readings and create false MAF readings on the output side of
MAF.  I plan to slowly convert the functions of the MAF over to the new
device.   I primarily want to ditch the platinum and heat sink fins in
the unit.   So I know I need to make false air speed and false
temperature readings.   
		
		Anyone have any good idea about this.   I would love to
eventually build this device and sell it for around $100.   I am also
thinking about adding a O2 sensor LED readout on the device and two
tuning knobs so you can play with values a little bit.  Conceivably the
device would hose clamp to the side the MAF.
		
		I am learning how to use an Atmel chip with 32 IO lines
which should be enough to pull data in from the O2 sensor and MAF and
then put out analog data to the MAf wires.  
		
		-- 
		Michael Stephens
		
		Electrical Engineering Student
		University of Wyoming
		http://students.uwyo.edu/falcon
		falcon at uwyo.edu or 89iroc at gmail.com 




	-- 
	Michael Stephens
	
	Electrical Engineering Student
	University of Wyoming
	http://students.uwyo.edu/falcon
	falcon at uwyo.edu or 89iroc at gmail.com 

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