Calculating Fuel Econ. from pulse times and mph

[Mike Dillon]

The vacuum control actually holds the pressure across the injector constant. 
In this case the injector duty cycle would be pretty good indication of the 
amount of fuel used. In the case where the presure with respect to atm. 
did not vary with manifold vacuum, the presure across the injector would 
vary and the duty cycle would be an inacurate measurment of fuel flow. 
(unless you did the fuel flow MAP duty cycle table thing)  I think this
is correct but I have an open mind.

Mike D




> From diy_efi-owner at esl.eng.ohio-state.edu Sat May  9 03:19 CDT 1998
> From: Daniel Ciobota <dciobota at hiwaay.net>
> X-Mailer: Mozilla 4.01 [en] (Win95; U)
> 
> I think I may have missed a few posts, so apologies if I repeat what's
> already been said.  IMHO, using the A/F ratio and air meter values is
> better than integrating injector duty cycles over time.  On my mustang,
> the fuel pressure is controlled by engine vacuum (on my race car, by
> boost as well), so, unless you've got your fuel pressure curve worked
> out pretty well, your calculations may contain significant error.  Also,
> I may be wrong but I believe the ford injectors are rated at 39psi, 100%
> duty cycle (what is called the static point of the injector).
> 
> 
> Daniel
> 
> 
> Clare Snyder wrote:
> 
> > Roger Heflin wrote:
> > >
> > > Hello,
> > >
> > > I have been trying to calculate fuel econ. from injector pulse
> > times.
> > > I have a batch fire vehicle, I believe I know what the number of
> > times
> > > per rpm that the injectors fire.  I think the injecotrs fire once
> > per
> > > rpm (is this right).  I know the injector rating (lb/hr), there ford
> >
> > > svo injectors which I believe means they are rated at 39 psi, my car
> >
> > > is running at 45 psi, so the injectors are doing 45/39 * 30 lb /hr.
> > > Also the computer says the injecotr is on x.x ms.  I am assuming
> > that
> > > is what the computer it telling the injectors to do.  Are the ramp
> > > up and ramp down times similar enough that you can assume that that
> > > time is close enough, or are there some transient things that cause
> > > the actual open time to be less than or greater than that number?
> > > What I am really tring to do is figure out what the absolute best
> > > gas mileage my car could get, if it was only crusing, with no
> > braking
> > > or acceleration, and also determine how badly different things
> > affect
> > > the gas mileage.
> > >                                 Roger Heflin
> > >
> > What you want to do is determine the ACTUAL fuel usage, as well as the
> >
> > ELECTRICAL time on of the injectors, then calculate the amount of flow
> >
> > per second of injector on time. Then all you have to do is have your
> > computor, or whatever you are using, add this given fuel amount every
> > second of real time. By inputting distance into the equasion, you can
> > get MPG as well as GPH consumption. The CompuCruise system did this
> > and
> > was very accurate after a good calibration run. For a simple fuel
> > totalizer, a calculator can be used. Have a circuit sum the injector
> > on
> > time, resetting every totalled second, with the reset closing the= key
> >
> > of the calculator. 0+(constant)=======. The constant is the # of
> > partial
> > gallons consumed per injector second. Every time the + key is closed,
> > it
> > gets added to the total. As for the circuit to time the "injector on"
> > time, I can't help you, but lots of EEs out there surely can come up
> > with something complicated, or mabee even simple:}
> > --
> >                                _/\_
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> 
> 
> 
> 
>