In article >,
SoCalMike > wrote:

> wrote:
> > Given ever higher price for gas it would be nice to be
> > able to monitor ones driving habbits to get the best MPG
> > posible.
> >
> > In a EFI engine the fuel consumption is based on the on
> > time for the injector(s). Has anyone seen any DIYS circuits
> > for intergrating the injector duty cycle.
> >
> > I have been playing with a laptop PC versio, but it isn't
> > too healthy to be watching a LCD while driving.
> >
> > I am hoping to find a way to reduce this info to a single
> > analog meter so that all you have to do is maximise or
> > minimisethe needle position.
> >
> > Terry
> >
>
>
> i believe a simple vacuum gauge hooked up to a port on the intake
> manifold might do the trick, or at least be worth playing around with.
> the less the vacuum, the better the mileage?

No. You can not relate between vacuum and milage. It doesn't take into
account airspeed and engine efficiency. You'd get much better milage in
top gear with a high manifold pressure than you would in bottom gear
with a low manifold pressure. One of the big reasons that a MT can get
better milage than an AT is that you can keep the RPMs low while opening
the throttle more.

Milage computers calculate your speed per rate of fuel injection and
integrate that to produce an average. It's simple and exact.