>Roger Bowman wrote:
>>
>> I saw the same thing when I played digifant recently.  It looks like a
>> little "blow-out" valve or reed valve.
Dave said:
snip
>        There is no need for a barometer because the FI system is not
>interested in air density, it's interested in the mass so the ecu can
>compute the correct amount of fuel for the proper stociometeric ratio.
>A barometer isn't going to help the ecu discern altitude (and thus the
>amount of oxygen in the incoming air stream) as barometric pressure
>varies as much due to the weather as due to altitude if I remember
>correctly. Some sort of O2 sensor pre combustion might help with
>this, but it would have to be another type of O2 sensor as the ones
>in cars work by having a different amount of oxygen on the two sides...
>
>dave

From the Bosch publication on the KE-Jetronic system (CIS-motronic, caveat
- no AFM as in Digifant, but does ahave a sensor plate which measures the
amount of air drawn into the engine)

"Adaptation of the air-fuel mixture at high altitudes.

"The low density of the air at high altitudes necessitates a leaner
air-fuel mixture.

At high altitudes, due to the lower air density, the volumetric flow
measured by the air-flow sensor corresponds to a lower air-mass flow.
Depending upon the facilities incorporated in the particlualr KE-Jetronic,
this error can be compensated for by correcting the injection time.
Over-enrichment is avoided and, therefore, excessive fuel consumption at
high altitudes.

The altitude compensation is provided by a sensor which measures air
pressure. In accordance with the prevailing air pressure, the sensor inputs
a signal to the ECU which changes the pressure actuator current
accordingly. This alters the lower chamber pressure, and therefore the
pressure difference at the metering slits, and this results in a change in
the injected fuel quantity.
It is also possibel to incorporate continuous adaptation of the injected
fuel quantity according to the changing air pressure"

Alistair