Fuel injection (contd.)
~
~
+30
·n . n
~
§0.65L
◊
Calculation of fuel injection time
To.
determine
how much fuel has to be injected into
each intake manifold, the ECM calculates the air
mass drawn into each cylinder.
The calculation is performed as follows: (each cylin-
der in the B234L engine has a capacity of 0.65 litres):
0.65 litres of air having a certain density has a definite
weight. Its density is calculated on the basis of intake
manifold pressure and temperature.
The ECM keeps the injection valve open until the cor-
rect amount of fuel has been injected in relation to the
measured air mass.
By means of the front heated oxygen sensor, fuel in-
jection time is corrected so that Lambda
=
1.0 is ob-
tained. The closed loop is disconnected during heavy
acceleration and full-load enrichment is activated for
maximum performance. A richer mixture is supplied
during acceleration and a leaner mixture during de-
celeration. For cold starting and during the engine
warm-up period before the closed loop is activated,
coolant temperature dependent fuel enrichment
takes place.
With a warmed-up engine and normal battery volt-
age, fuel injection duration will vary between about
2.5 and 3.5 ms at idling speed, depending on the en-
gine version. At wide open throttle,. fuel injection
duration is about 18 ms.
Saab 9000
Technical Description 43
I
229
589
206a
(CYL1) 3
1 2
µp
206b1CYl2l •
µp
206CtCYL3l
5
µp
µp
G7P
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