Operating instructions

1998 Volvo S90
SFI is all-electronic and microprocessor-
controlled. It can continually compensate for
variations in engine load, speed and temperature
to give the best economy and power. An
important feature of the system is a mass air flow
sensor that measures the mass of the inducted air
instead of the volume. In this way the system can
make instantaneous adjustments for changes in air
temperature or density, thus always assuring the
best economy with the lowest possible exhaust
emissions.
Heated oxygen sensor
This is an emission control system designed to
reduce emissions and improve fuel economy. The
heated oxygen sensors monitor the composition of
the exhaust gases leaving the engine. The exhaust
gas analysis is fed into an electronic module. This
adjusts the air-fuel ratio to provide optimum
conditions for combustion and efficient reduction
of the three major pollutants (hydrocarbons,
carbon monoxide and oxides of nitrogen) by a
three-way catalytic converter.
Air pump system
During cold starts, an electric pump is activated
which directs air to the exhaust channels. This
initiates a secondary combustion of exhaust gases
which helps minimize hydrocarbon and carbon
monoxide levels and reduces warm-up time for
the three-way catalytic converter. The pump
begins to function when the engine is started. It
remains in operation until the three-way catalytic
converter has reached normal operating
temperature. A sound may be audible from the air
pump during this warm-up period. This is normal.
When idling, the air pump performs a self-
diagnosis. A soft whining noise can be heard,
which is also normal.
Emissions systems pg. 113
Evaporative control system (EVAP)
The engine is equipped with a fuel evaporation
system which prevents the emission of fuel vapor
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