[Diy_efi] Newbie with a simplified Motronic project

[Eric D Byrd]

to GAS,

On Sun, 27 Oct 2002 13:59:39 -0600 "arnie" <arnie_ at charter.net> writes:
> The MAF system will self compensate for changing in engine VE as the
> mileage/wear take it's toll.  As engine wear would occur, a SD setup 
> would
> need to be 'retuned' to compensate for changes in engine efficiency.

But only in open loop, right?  In closed loop, O2 governs mix via
feedback.  And here is something I wonder.  As wear occurs, VE drops,
right?  And that means for a given tuned fuel pulse, the air actually
available drops, which would tend to richen the mix and make emissions
worse, but not necessarily reduce power.  Do you get more specific power
from fuel when it burns stoich?  Or is it pretty much the same when you
have less oxygen than you need?  I guess it would depend on reaction
energy of fuel to CO2, vs. fuel to CO.

> 
> GAS
> 
> ----- Original Message -----
> From: "Eric D Byrd" <klox at juno.com>
> To: <diy_efi at diy-efi.org>
> Sent: Saturday, October 26, 2002 11:13 PM
> Subject: Re: [Diy_efi] Newbie with a simplified Motronic project
> 
> 
> > I think all you need for basic fuel and ignition control is MAP, 
> IAT and
> > RPM.  The reason MAF is good is that it accounts for both pressure 
> and
> > temperature.  An accurate MAF signal, interpreted by an accurately 
> tuned
> > ECU table, is just as good as MAP + IAT interpreted by an 
> accurately
> > tuned ECU table.  Consider the equation of state, that it has 
> three
> > variables, pressure, temperature and density.  Fix pressure and 
> temp, and
> > you have density.  What an ECU really wants is an accurate measure 
> of
> > density, because that's how you set fuel mixture.  And to set 
> timing, you
> > need to know density and water temp, because the fireball burns at 
> a rate
> > dependent on density and temp in the chamber at TDC.  Essentially
> > dependent on what is known as the "second speed of sound", a term
> > applicable usually only to heat transfer issues in engineering.  
> With
> > those in mind, I still wonder why they bothered with making an MAF
> > sensor.  It isn't more accurate, simply because all your accuracy 
> rests
> > on the accuracy of your tune in your ECU.
> 
> > --Eric Byrd
> 
> 
> 
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> 


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