Modes of Operation

Diagnostic Test 2 (Part 1 of 2). 1983 4-151/2.5L:

Diagnostic Test 2 (Part 2 of 2). 1983 4-151/2.5L:

EXCEPT 1983-86 4-150 Open Loop Mode of Operation
The engine will be in this mode (or variation thereof) whenever the engine operating conditions do not meet the programmed variables necessary for Closed Loop Mode of Operation.
During Open Loop Mode of Operation, Fig. 4, the air/fuel mixture is maintained at a programmed ratio that is dependent on the engine operating conditions. The oxygen sensor data is not used during this mode of operation. The following conditions involve either Open Loop Operation or a variation thereof:
1. During engine start-up.
2. When engine coolant temperature is too low.
3. When oxygen sensor temperature is too low.
4. During wide open throttle (WOT) operation.
5. When engine is running at idle speed.
6. When battery voltage is too low.

Closed Loop Mode Of Operation
The engine will be in this mode when all the input data meets the programmed variables for Closed Loop Mode of Operation, Fig. 4, and the output from the oxygen sensor is used by the MCU. This will result in an air/fuel mixture that will be optimum for the engine operating condition and also will correct any preexisting too lean or too rich mixture conditions.
A low oxygen content in the exhaust indicates a rich air/fuel mixture, and a high oxygen content indicates a lean air/fuel mixture. The optimum air/fuel mixture ratio for the most efficient conversion of HC, CO and NOx is 14.7:1.