>> >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.

>Faster airflow -> lower pressure ! In the manifold that is.

Consider this situation:

A regular carbureted engine is driving uphill at a moderate speed
(constant) and with a medium throttle setting.

In the intake manifold we have, say 0.7 bar.

Then the driver open up the intake valve by applying full throttle.
The pressure in the manifold now increase to, say 0.9 bar.

Why? 

This happens because the pistons are moving with the same speed as 
before the throttle was applied, but the air intake is now wide open.

If you have ever looked at a regular vacuum economy gauge, you
must have noticed that it will show "good economy" when running 
at idle, but if you stop the engine it will show "bad economy"..

There is no doubt that the pressure in the intake manifold is 1 bar with the
engine stopped..?

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

Still disagree?

-Oyvind