Ford Corsar Repair Manual page 261

CLOSED LOOP
CONTROL
E.CX.S.
, - ' ,
Injector
Engine
SEF639B
E.C.C.S. SYSTEM DESCRIPTION
pq
Fuel lnjection Control (Cont'd)
MIXTURE RATIO FEEDBACK CONTROL
Mixture ratio feedback system is designed to precisely control
the mixture ratio to the stoichiometric point so that the three-
way catalyst can reduce CO, HC and NOx emissions. This
system uses an exhaust gas sensor in the exhaust manifold to
check the air-fuel ratio. The control unit adjusts the injection
pulse width according to the sensor voltage so the mixture ratio
will be within the range of the stoichiometric air-fuel ratio.
This stage refers to the closed-loop control condition. The
open-loop control condition refers to that under which the E.C.U.
detects any of the following conditions and feedback control
stops in order to maintain stabilized fuel combustion.
1) Deceleration
2) High-load, high-speed operation
3) Engine idling
4)
Malfunctioning of exhaust gas sensor or its circuit
5)
Insufficient activation of exhaust gas sensor at low engine
temperature
6) Engine starting
MIXTURE RATIO SELF-LEARNING CONTROL
The mixture ratio feedback control system monitors the mixture
ratio signal transmitted from the exhaust gas sensor. This
feedback signal is then sent to the E.C.U. to control the amount
of fuel injection to provide a basic mixture ratio as close to the
theoretical mixture ratio as possible. However, the basic mix-
ture ratio is not necessarily controlled as originally designed.
This is due to manufacturing errors (e.g., air flow meter hot
wire) and changes during operation (injector clogging, etc.) of
E.C.C.S. parts which directly affect the mixture ratio.
Accordingly, a difference between the basic and theoretical
mixture ratios is quantitatively monitored in this system. It is
then computed in terms of "fuel injection duration" to automat-
ically compensate for the difference between the two ratios.
Injection pulse
No.
1 cylinder
No. 2
c y l i n d e r d
No.
3
cylinder
A
No. 4 cylinder
A
t-----l
engine cycle
----A
SEF976E
FUEL INJECTION TIMING
Fuel is injected once a cycle for each cylinder in the firing order.
When engine starts, fuel is injected into all four cylinders
simultaneously twice a cycle.
No. 1
cyl i n der-
No.
2
cyl i n der-
-
1
No. 3 c y l i n d e r - I
I - -
1 engine cycle
-----A