i uderstand the purpose of 02 sensor. can you explain the cycling function ? i believe it reads about .45 V in data stream and that is 14.5/1 or stoich. if richer the V read out is higher? what is the need for it to cycle above and below? does it cycle above and below the actual A/F or just cycle above/below stoich and report the fact engine is lean rich to ECU but not how lean rich? does it provide a continuous signal to ECU? if so in open loop the ECU simply disregards and runs off of constants/values provided ?? when AE is envoked it appears itwould read the enrichment from 02 sensor but simply disregard it. same with PE? if i envoke AE or PE i would assume in aldl it would show in my samples that occuring and directly proportionite to TPS position(volts) as well?
comments?

 

The higher the O2 sensor voltage the richer the AFR is. This is as long as the engine is running OK and the sensor is up to temperature.

The cycling of the AFR and resultant cycling of the O2 sensor is based on a series of calibration tables. These tables contain the target O2 sensor values along with delays and gains. The fueling loop uses these values along with the O2 sensor voltage to 'close the loop'.

The actual AFR cycling is mostly for cat-con operation. The fueling loop proportional gains are set high in order to force the loop to oscillate. This provides a rich/lean exhaust gas so the cat-con can properly reduce pollutants.

The signal from the O2 sensor to the ECM is constant. The '747 ECM reads the O2 sensor value 80 times a second. From this value another lagged value is created. By comparing the two values the ECM knows whether the O2 is reporting lean or rich, and in what direction it is moving.

An example would be if the lagged O2 value is higher then the current O2 value, the ECM knows that the AFR is moving leaner. Then if the current O2 value is lower then the lean set point, the ECM knows that the AFR is lean and going leaner still.

The '747 ECM also creates an error term from the current O2 sensor value and a set of calibration tables. This provides a term of how far from the desired set point the AFR actually is. It is used for INT update delays, proprtional gains and duration, and other assorted stuff.

Open loop ignores current O2 sensor operation. But will still use saved BLM adjustments. PE mode is a pseudo open loop mode. It will add fuel from a BLM cell, but not remove fuel.

AE will affect the O2 sensor reading and the ECM will compensate for it. The '747 has an option flag that can be used to have the INT reset whenever AE is entered. But it is not perfect.

Over on the diy-efi site there is a paper that describes the '747 fueling routine. It is a little dated but a good reference.

RBob.