Closed loop fuel system

Geoff’s question:

Should a vehicle fuel system be in closed loop using the oxygen sensor all the time or does it switch between closed loop and open loop depending on load/rpm.”


Thee fuel system should be in closed loop all the time AFTER the engine has reached normal operating temperature. If it ever drops out of closed loop into open loop during normal driving after the engine has warmed up, then there’s a problem in the vehicle that should be checked out (such as a bad thermostat or bad temperature sending unit.)

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