computer project

Zublin, Bryan (SD-MS) BZUBLIN at
Sat Jun 17 02:13:38 GMT 1995

Roberto L. Landrau      landrau at writes:

> With
> constant fuel pressure, I presume the flow rate is proportional to
> the pulse width, offset by the injector "dead" or "turn-on" time.
> The fuel pressure in my car varies as a function of vacuum (or intake
> air pressure) level.  Would I have to add a fuel pressure sensor in
>order to compute fuel flow?

You need to determine the "duty cycle" of the injectors to calculate the 
flow rate.  For example, if an injector is firing every 10 mS, and the ON 
pulse width is 1 mS, the duty cycle is 10%.  Therefore, it is flowing 10% of 
its maximum flow rate (this ignores the dead time).  Of course, you need to 
know what the maximum flow rate of the injectors is in order to complete the 
calculation.  This can be measured if you have an injector, fuel pump, and 
pressure regulator.

I think that you can assume that the pressure is relatively constant, 
because most EFI systems have a fuel pressure regulator that is referenced 
to the intake manifold (I think this is what you were referring to).  This 
maintains the same pressure across the injector.

Bryan Zublin
bzublin at

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