In addition to promoting efficient combustion and catalyst operation, a stoichiometric air/fuel ratio also promotes excellent fuel economy. This relatively lean mixture is desirable during cruise and idle operation; however, other operating conditions often require a richer air/fuel ratio. When the electronic control system ignores signals from the oxygen sensor and does not correct the air/fuel ratio to 14.7:1, the system is said to be operating in open loop.
In order to prevent overheating of the catalyst and ensure good driveability, open loop operation is required under the following conditions:
• During engine starting
• During cold engine operation
• During moderate to heavy load operation
• During acceleration and deceleration
During open loop operation, the ECU ignores information from the exhaust oxygen sensor and bases fuel injection duration calculations exclusively on the other input sensors.
Was this article helpful?