programming for a MAF based system

Justin Becker jgbecker at kent.edu
Thu Mar 28 08:50:07 GMT 2002


It is my understanding that the Ford EEC-IV mass-air engine control system
references the BAP (ambiant manifold pressure) only at start-up, before the
engine cranks. I beleive it is to determine air density (altitude in a way)
to minimize emissions, and make the car run better in every situation. Is
this true? Is there a way for the BAP to be referenced more often in the
case of adding positive manifold pressure (super/turbocharging)? How did the
Supercoupes reference boost (manifold pressure) in order to supplement
control of the air/fuel ratio as well as timing; if they did at all? Anyone
have any clues?
Also, what is ISV?
Justin

----- Original Message -----
From: "Perry Harrington" <pedward at apsoft.com>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, March 26, 2002 3:11 AM
Subject: Re: programming for a MAF based system


> Hello,
>
> I'm new to the list, so if you're perplexed as to who I am, that's why.
>
> For a MAF system you want MAF, TPS, ACT, BAP, ECT, ISV, and RPM.
> Here's the reason:
>
> You want to reference MAF to RPM to infer VE.  Once you know VE,
> you can key in a table, just like MAP does.  The other reason is
> because you can make an even simpler inference:  Have a global
> that defines your lb/hr per HP.  With the MAF vs RPM you can calulate
> realtime HP and use that to simply find your base fuel pulswidth.
>
> This makes for very simple integer math with table lookups if you
> want.
>
> Then add the O2 sensor to fine tune the mixture.
>
> The other sensors I'd use are BAP (baro), constantly to adjust for
> altitude, ACT for additional spark advance and air density, and
> ECT for input to lean/richen the mixture so as to obtain the desired
> engine temp. The BAP is important especially on turbo cars, because
> turbos were intended for altitude compensators.
>
> Ford uses the ACT for advance, ECT vs VE for AFR, and BAP to compensate
> for altitude.
>
> I postulate that it is possible to design a fuel injection computer and
> program that will tune an engine without user input, just give it gross
> values and it'll fine tune it.  The only thing I'd add to do that is an
> engine mounted accelerometer and MAP sensor.
>
> The accelerometer would be used to sense the roughness of the engine,
> and the MAP to sense vacuum; so you can adjust the mixture like you would
> with a conventional vacuum gauge.  Find the mixture that provides the
smoothest
> idle and highest vacuum.
>
> --Perry
>
> On Thu, Mar 21, 2002 at 03:15:38PM -0500, Eric Fahlgren wrote:
> > les wrote:
> > >
> > > Can someone point me to any hints for how to approach the
> > > algorithms for fuel calculations, as they apply to a mass air
> > > flow measuring fuel system?
> > >
> > > At first look, it seems that all the 'normal' variables needed for
> > > MAP systems just drop out of the equation. I suppose that I still need
> > > a 2d map , to allow for richening under boost, but it just seems too
> > > simple. I mean, other that for idle speed needs, rpm doesn't even seem
> > > to enter the equation. Air mass is air mass.
> > > I understand that the MAF is not linear, but a simple lookup table
> > > should
> > > fix that.
> >
> > Les,
> >
> > Are you working with a true _MASS_ air meter, not an AFM which
> > produces some uncorrected value?  In that case, just have a 1D
> > map which relates mass to AFR and from that calculate a pulse
> > width.  If not, you need temperature correction (at least) to
> > get mass, then use the table.  Should be pretty simple compared
> > to the 2d VE tables usually used with speed density.
> >
> > All the usual gamma terms still apply same as with MAP systems,
> > acceleration enrichment, cold start/warmup and so on.
> >
> > Eric
> >
> > ----- End of forwarded message from owner-diy_efi at diy-efi.org -----
>
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> --
> Perry Harrington             Linux rules all OSes.               APSoft
()
> perry at apsoft dot com                  Think Blue. /\
>
> Those who would give up essential liberty to purchase a little temporary
safety
> deserve neither liberty or safety. Nor, are they likely to end up with
either.
>                              -- Benjamin Franklin
>
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