idea..

Mark Pitts saxon at zymurgy.org
Tue Oct 7 14:28:01 GMT 1997




On Tue, 7 Oct 1997, John Hess wrote:

> 
> 
> > ----------
> > From: 	Paul Raley[SMTP:raleyp at UDel.Edu]
> > Sent: 	Monday, October 06, 1997 10:07 PM
> > To: 	diy_efi at coulomb.eng.ohio-state.edu
> > Subject: 	Re: idea..
> > 
> > 
> > 
> > > someone mentioned trying to locate fuel flow meter to use for a
> > mileage
> > > calculator.  Why not have the ecu record the combined pulse width
> > over a
> > > period of distance, based on the assumption that fuel pressure
> > remains
> > > fairly constant, a certain distance traveled divided by the time the
> > > injectors are open == MPG. All is needed is a pulse input from oneor
> > more
> > > of the wheels,  each pulse = a certain distance ,and the frequency
> > is the
> > > speed.
> > 
> > why could you assume the fuel pressure remains the same?  on my
> > nissan, not
> > only does the fuel pressure regulator (which not everyone has) alters
> > the
> > pressure, but the ECU controls the voltage of the pump, thereby
> > varying
> > pressure from 20psi to 60psi or more.   Don't other modern ECU's
> > control the
> > fuel pump voltage?
> > 
> > If you have a digital dash as on the nissan, the speed sensor could be
> > used.
> > This transmits two pulses for every revolution (optical).  The analog
> > dash
> > uses the same setup except that its magnetic and located in the dash
> > itself.
> > There are a number of Z's in the junkyard with these sensors located
> > next to
> > the battery under the speed control device.
> > 
> > Paul R.
> > 
> The GM unit varies the pressure according to vacuum (manifold pressure).> 
> 

That is to maintain fuel pressure relative to the manifold, else it would
get v rich as you shut the throttle, kinda like sucking on a straw.

Mark




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