idea..

[Clare Snyder]

>
>
>> ----------
>> 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).
>
>
>
>
Only varies absolute pressure so relative pressure(pressure across the
injector) remains constant. Without this adjustment you would have a problem
- with it there is no problem. It is like an altitude compensator - not
exactly, but close.