>> >> >These, as do most "economy gauges" use a pressure sensor on the
>> >> >vacuum line of the engine. The harder the engine work the higher the
>> >> >vacuum. Very imperic.
>>
>> > -Oyvind replied
>> > >
>> >> Do you mean "less pressure" when you say "higher vacuum"?
>> >> If so, you are mistaken.
>> >>
>> >> If the engine works harder you get MORE pressure in the intake
>> >> manifold.
>> >>
>> >> Just think of it, when you step on the loud pedal you open the air
>> >> intake valve to allow more air into the engine. More air -> Higher
> pressure.
>>

[Snip]

>> There is also no doubt that the pressure is less than 1 bar when
>> running at idle?
>>
>> Still disagree?
>>

>The so called 'Economy Gauges' are a total waste of time - they flop
>backwards and forwards crazily.  The tendency of car makers to omit
>RPM gauges in favour of theses devices is idiotic - a car computer
>might make sense of manifold pressure, but its useless info to a
>person.

Yes, I totally agree with you.
The principle is more or less correct, but the output (visual) is not
directly proportional to fuel consumption, and it has no relation to
mpg.

But it does tell you what happens with the pressure in the intake manifold
when applying throttle, and that's what I'm discussing.

-Oyvind