Quote:
Originally Posted by ToronadoGuyDenver
Also, when should the loop be closed and/or open?
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Open loop is used before the O2 sensor warms up and during wide open throttle acceleration. Once the O2 sensor reaches operating temperature, it starts sending out a varying voltage signal that is used by the computer to correctly set the pulse width on the mixture control solenoid. This is closed loop since the measurement is used to directly control the mixture. Unfortunately, the O2 sensor can cool off at idle, even with the engine at operating temp, which causes the system to go back to open loop. You can ensure the O2 sensor is at temp by running the engine at 2000 RPM for a couple of minutes. With a dwellmeter hooked up to the green test terminal, you should see the M/C solenoid dwell varying at idle when the O2 sensor is warmed up. If not, there's a problem.