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Home >> Jeep >> 1983 >> Cherokee Base, 4.2 C, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> 4.2L Feedback Carburetor System >> Operation >> Microcomputer Control Unit >> Open Loop
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Open Loop

In this mode, the MCU determines the air/fuel mixture based upon engine operation rather than oxygen sensor input signals. There are 5 open loop modes of operation and each has a specific metering pin position.

However, because more than one condition may exist at any time, the MCU is programmed with a priority ranking for each operation. The MCU complies with the highest priority. The open loop priorities (listed from highest to lowest) are as follows: Cold Weather Start-Up, Open Loop 2 (Wide Open Throttle), Open Loop 4 (Low Manifold Vacuum), Open Loop 3 (Low Ported Vacuum), Open Loop 1 (Cold Engine Operation).

NOTE: With each engine start-up, a start-up timer is activated. During this interval, if engine operating condition would otherwise trigger normal closed loop operation, OL1 mode is selected.
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