Fuel Feedback Systems; Computerized Emission Control Fuel Feedback Systems - Jeep 1987 Wrangler Workshop Manual

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mm. FEEDBACK SYSTEMS
COMPUTERIZED EMISSION CONTROL (CEC)
FUEL FEEDBACK SYSTEMS
The C E C Feedback System for six-cylinder
engines controls undesirable emission to the
atmosphere and maintains an ideal air/fuel ratio
to provide an optimum balance between
emission control and engine performance.
This is accomplished by the use of a micro com-
puter unit (MCU), several MCU input compo-
nents and several MCU output components.
This system uses the micro computer unit
(MCU) to monitor various engine operating
conditions.
Based on these conditions, the MCU may,
depending on the mode of operation, generate
output signals to provide the proper air/fuel
mixture, proper ignition timing and engine idle
speed.
E a c h s y s t e m operates in two modes of
operation: closed loop and open loop.
Closed loop operation occurs when the air/fuel
ratio is varied according to the oxygen content in
the exhaust gas.
During open loop operation, the air/fuel ratio is
predetermined by the MCU for several engine
operating conditions, such as:
# start-up
• cold engine operation
e wide open throttle (WOT) engine operation
W h e n the e n g i n e is s t a r t e d , the M C U
determines which mode of operation (closed
loop or open loop) is correct.
It can determine this by monitoring the input
signals from the various input components.
Air and coolant temperature information, engine
RPM information and vacuum levels are all
provided to the MCU for this determination.
The MCU operates the system in the open loop
mode based on a priority rating for the various
predetermined engine operating conditions.
It continues to operate the system and the
output components in the open loop mode until
such time when the engine operating conditions
indicate that the closed loop mode of operation
is appropriate.
At this time, the MCU shifts the operation to
closed loop.
Based upon the oxygen content in the exhaust
gas and other inputs, it continues to operate the
system in the closed loop mode and constantly
varies the air/fuel ratio to maintain an optimum
14.7:1 ratio.
As the engine operating conditions are
constantly monitored by the MCU, any change
in condition such as the engine being placed in
wide open throttle (WOT) operation, is quickly
detected by the MCU.
The MCU then places the system back in the
appropriate open loop mode of operation.
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