1983 Jeep Cherokee Base, 4.2 C, AutomaticFACTORY OEM SERVICE PROCEDURE

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.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.