Fuel pressure is no problem and can be done accurately.  Static (100%) flow 
capacity is easy to calculate using one of the injectors in a measuring cup 
and a timer.  And btw, I am not recommending anyone do this -- all 
disclaimers apply.  But the important thing here is that the volume of fuel 
that has flowed is not proportional to the injector pulse width due to the 
times that the injector is opening and closing.  Apparently it is significant 
due to the frequency at which the injector pulses.  But yes, this can be 
calculated for.  It's not difficult, but will take a bit of time on a bench.

Cheers,
-Neil.



On Tuesday 08 August 2006 12:32, Martin K wrote:
> I helped a guy work on a custom ECU for a formula SAE car last year so I
> know a little bit here.
> What you need to know as you already said is fuel pressure, pulse width,
> and flow capacity.
> The only thing not known by the ECU is fuel pressure, correct? So you
> would have to add a pressure transducer, but fuel pressure should be
> relatively constant, shouldn't it? Flow capacity is a constant.
> Tapping onto the fuel injector signals wouldn't be that hard to do
> considering they're already clamped against inductive spikes by the ECU
> drive circuit.
> --
> Martin K
>
> PicDude wrote:
> > That's probably because they're very specific to each vehicle and require
> > some detailed knowledge of the vehicles.  MPG = distance / fuel flow, but
> > fuel flow is not measured for many reasons -- accuracy of flow meters,
> > cost of flow meters, return-style fuel systems dump back some of that
> > fuel into the tank, etc.  Instead, flow is calculated from fuel pressure,
> > injector pulse widths, and injector flow capacity.  The pressure
> > difference between the fuel rail and intake manifold is irrelevant since
> > the fuel-pressure regulator is referenced off the manifold pressure, so
> > it's always relative.  The vehicle manufacturers know all this info.  If
> > you know this info, or have some way to calibrate the fuel flow in the
> > vehicle, it should be easy to create one of these.
> >
> > I've been meaning to build one of these (for some years now), but
> > gathering that info has held me back.  If someone has easy access to this
> > or wants to do the math, then I'd be game for getting involved with this.
> >
> > Cheers,
> > -Neil.
> >
> > On Tuesday 08 August 2006 11:54, John Ferrell wrote:
> >> &expletive: Sorry, I forgot the tag the first time...
> >>
> >> I am not having any luck finding an aftermarket computer for gasoline
> >> consumption with Google.
> >>
> >> The one that is factory installed in my 2001 Chrysler Minivan works very
> >> well.
> >>
> >> The intended target install is a Winnebago (1999 Ford 350-V10 engine).
> >>
> >> I was hoping to find something off the shelf with a DIY install. I would
> >> consider a project, but my completion rate has been pretty poor lately.
> >>
> >> I think AVR has a contest for the Butterfly that is still open. How
> >> about one of you fellows with the smarts & ambition execute this project
> >> & win the contest? John Ferrell    W8CCW
> >> "My Competition is not my enemy"
> >> http://DixieNC.US
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