Open Loop Mode

Switch Calibrations. 1982 4-151:

The engine is in this mode of operation when:
a. Starting the engine and the engine is cold or air cleaner air is cold.
b. Engine is being decelerated to idle from partial throttle or is being accelerated to partial throttle from idle position.
c. Carburetor is at or near wide open throttle.

Each operation has a specific air/fuel ratio and because more than one of the engine operational selection conditions can be present at one time, the MCU is programmed with a priority ranking for the operations that comply with the operation having the highest priority. These priorities are described below:

Cold Weather Engine Start-Up and Operation
If the air cleaner air temperature is below the calibrated value of the thermal electric switch (TES), the air/fuel mixture is at a rich ratio. Lean air/fuel mixtures are not used for a preset period following a cold weather start-up.

At Or Near Wide Open Throttle Operation (Engine Cold)
This mode of operation occurs whenever the coolant temperature is below the calibrated switching temperature of the open loop coolant temperature switch, Fig. 7, and the wide open throttle vacuum switch (cold) has been closed due to a decrease in manifold vacuum (less than 5 inches Hg). When the engine is in this mode of operation, the mixture control (MC) solenoid provides a rich air/fuel mixture for cold engine operation at wide open throttle.

At Or Near Wide 0pen Throttle Operation (Warm Engine)
This mode of operation occurs whenever the coolant temperature is above the calibrated switching temperature of the enrichment coolant temperature switch and wide open throttle vacuum switch (warm) has been opened because of the decrease in manifold vacuum (less than 3 inches Hg). When the engine is in this mode of operation, the MC solenoid provides a rich air/fuel mixture for warm engine operation at wide open throttle.

Adaptive Mode Of Operation
This mode of operation occurs when the engine is either at idle speed, accelerating from idle speed or decelerating to idle speed. If the engine rpm, (tach) voltage is less than the calibrated value, and manifold vacuum is above the calibrated switching level for the adaptive vacuum switch (switch closed), an engine idle condition is assumed to exist.

If the engine rpm (tach) voltage is greater than the calibrated value and manifold vacuum is below the calibrated switching level for the adaptive vacuum switch (switch open), an engine-from acceleration-from idle speed condition is assumed to exist.

If the engine rpm (tach) signal is greater than the calibrated value and manifold vacuum is above the calibrated switching level of the adaptive vacuum switch (switch closed), an engine-deceleration-to-idle speed condition is assumed to exist. During the adaptive mode of operation, the MC solenoid provides a predetermined air/fuel mixture.