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Open Loop vs Closed Loop
You might notice upon a/f gauge installation that the o2 readings are erratic at anything but a wide open throttle blast. We will explain this. Under ordinary conditions the car's ECU will read data from the o2 sensor in order to determine how much fuel to put into the engine to achieve
the optimum fuel ratio. When the o2 sensor reads above or below 0.450 volts the ECU will automatically adjust the fueling to try and reach that optimal voltage. This happens very rapidly, several times per second. The readouts from the o2 sensor can drop as far down as 0.20 volts or as high as 0.80 volts. So when you look at the a/f gauge, the lights are bouncing
up and down. This continuous feed back process is called closed loop operation. For open loop operation to happen the ECU has to detect a predefined throttle position (usually around 80%). Under open loop operation the ECU will ignore the o2 sensor output and simply
work from a predefined code in the ECU. In the case of a stock ECU this will give you quite a rich readout on the a/f gauge. This is where your power is found. If youcan use aftermarket tuning devices such as SAFC to richen or lean what information the ECU gets fed, you can change
the open loop fuel curve. Unfortunately most a/f gauges and o2 sensors are not of a high enough resolution to make accurate and repeatable readings for maximum horsepower.
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