Porsche 928 S 1986 Driver Manual page 68

Carbon monoxide and unburned hydrocarbons
are converted into harmless carbon dioxide
and water. The oxides of nitrogen react with
carbon monoxide to form carbon dioxide and
nitrogen which accounts for about 80 % of the
air we breathe.
For optimum operation of the catalytic con-
verter it is essential that the catalytic acti-
ve surface is retained. For this, it is essential
that only unleaded fuel be used.
Leaded fuel leads to rapid ageing of the cata-
lytic converter since the lead in the fuel appears
in the form of a gas, becomes embedded in
the surface and thus blocks the catalytically
active noble metal.
The lambda sensor is very important for the
full effect of the catalytic converter. It is install-
ed in the exhaust pipe before the catalytic con-
verter and continuously measures the exhaust
gas composition.
The catalytic converter is only able to convert
all three pollutants if the engine is operated
with the theoretically correct air-fuel ratio. The
electrical signal from the lambda sensor is
evaluated in the LH-Jetronic control unit and
the mixture is then adjusted to the optimum
value for the catalytic converter.
64
The tank ventilation system prevents fuel
vapours from escaping from the tank into the
atmosphere.
Fuel vapours from the tank are led into a
canister which is filled with active carbon .This
canister is purged while driving and the fuel
vapours are burned in the engine.
The system is maintenance-free and contri-
butes partly towards reducing the fuel con-
sumption.
Refuelling
The vehicle may be run only on unleaded
fuel to DIN 51607.
Fuel octane requirement:
regular fuel minimum 91 RON (82 MON)
If unleaded premium fuel is not available, a
built-in control system (knock and boost pres-
sure control) makes it possible also to refuel
with unleaded regular fuel with at least 91
RON (82 MON).
Running on unleaded regular fuel may result
in a slight loss of power and a slight increase
in fuel consumption.
Although the use of leaded fuel does not lead
to engine damage, it has a lasting effect on
the operation of the catalytic converter and
the lambda sensor. In addition to a deterio-
ration in the effect of the catalytic converter,
this may also lead to impaired driveability and
increased consumption.
Furthermore, the damage to the system can-
not be entirely cancelled out by subsequent
running on unleaded fuel.
For this reason, a tank filler neck of smaller
diameter with a flap is installed, which is in-
tended to prevent refuelling with leaded fuel
by mistake.
The flap can only be opened with the unleaded
pump nozzle.
Topping up with unleaded fuel from commer-
cially available fuel canisters is not possible.