Actron Ford Code Scanner CP9015 - Manual (Page 56)

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an electric motor (“Feedback
Carburetor Actuator”) to position this
rod.
• Another method uses a fuel metering
rod positioned by vacuum. The
computer controls vacuum to this rod
by using a “Vacuum Regulator
Solenoid”. The computer sends a
duty cycle signal (see definition in
Reference Glossary) to the solenoid
to vary vacuum.
• A third version has the computer
controlling air into the carburetor idle
and main system vacuum passages.
A “Feedback Control Solenoid” is
used to control air entry. A duty cycle
signal from the computer controls this
solenoid to vary air flow.
Hot engine cruise condition
“Closed Loop” operation
The computer uses the engine
temperature and throttle position
information to tell when the engine is all
warmed up and cruising. At this time the
computer will use the Exhaust Gas
Oxygen sensor to run the engine in a
“closed loop” mode for minimum
emissions and best fuel economy.
Cold start, Acceleration,
Deceleration and Idle
“Open Loop” operation
The computer runs the engine in an
“open loop” mode when sensor
information signals one of the driving
conditions listed above. The computer
relies on factory programmed instruc-
tions to determine the proper air/fuel
mixture to deliver.
MCU idle speed adjustment
The MCU system does not control idle
speed – a standard mechanical idle cam
mechanism is used. However, some
MCU systems have a vacuum operated
“Throttle Kicker” actuator. The computer
uses this device to push the throttle
linkage off idle position when additional
idle RPM is required. This happens
when sensors indicate a cold start or
engine overheat condition. The
computer energizes a “Throttle Kicker
Solenoid” to apply vacuum to the
actuator.
MCU spark retard
The MCU system does not control spark
timing – a standard distributor is used.
However, some MCU systems can send
a signal to retard timing if the knock
sensor indicates an engine knock
condition. The computer energizes a
“Spark Retard Solenoid” to bleed control
vacuum from the distributor advance to
retard the ignition timing.
MCU Controlled Emission Systems
• Thermactor Air System – All MCU
vehicles have this system which is
similar to the one discussed earlier in
this section. The MCU uses engine
temperature throttle position
information to determine proper
operation of the thermactor system.
• Fuel Evaporation Recovery System –
This system is similar to the one
discussed earlier in this section. It is
only used on some MCU vehicles.
The MCU uses engine temperature
and throttle position information to
determine proper operation of this
system.