Mechanism And Function; General; Air Flow Meter - Subaru XT 1988 Service Manual

2-7
FUEL INJECTION SYSTEM
MECHANISM AND FUNCTION
General
The Multi Point Fuel Injection (MPFI) system is a system
that supplies the optimum air-fuel mixture to the engine for
all the various operating conditions through the use of the
latest electronic technology.
With this system fuel, which is pressurized at a constant
pressure, is injected into the intake air passage of the cylinder
head. The injection quantity of fuel is controlled by an inter-
mittent injection system where the electro-magnetic injection
valve (fuel injector) opens only for a short period of time,
depending on the quantity of air required for one cycle of
operation. In actual operation, the injection quantity is
determined by the duration of an electric pulse applied to the
fuel injector and this permits simple, yet highly precise meter-
ing of the fuel.
Further, all the operating conditions of the engine are con-
verted into electric signals, and this results in additional
features of the system, such as large improved adaptability,
easier addition of compensating element, etc. The MPFI
system also has the following features:
1) Reduced emission of harmful exhaust gases.
2) Reduced in fuel consumption.
3) Increased engine output.
4) Superior acceleration and deceleration.
5) Superior startability and warm-up performance in cold
weather since compensation is made for coolant and intake
air temperature.
2
Air Flow Meter
The MPFI system employs a hot-wire type air flow meter.
This air flow meter converts the amount of air taken into the
engine into an electric signal by utilizing the heat transfer
phenomenon between the incoming air and a heating resistor
(hot wire) located in the air intake.
The features of this flow meter type are as follows:
1) High-altitude compensation is made automatically.
2) Quick response.
3) There are no moving parts.
4) It is compact.
Hot wire
Air flow
L2-889
Fig. 1