Originally Posted by
foama
Just for understanding:
The linear air-fuel ratio sensor (oxygen sensor) works practically in real-time, and in the OEM setup it is located where it can distinguish between the exhaust puffs of each cylinder. This is needed for the fuel-air trim of the individual cylinders.
Consequently, if the linear oxygen sensor would be located where it can only sense the exhaust gas from one particular cylinder, the precise air-fuel trim would only adapt to the injector of that one single cylinder, and not adapt individually to the two others. That creates the situation of the overall trim being off, and that in turn causes the code.
I'm finding this a very interesting discussion. Foam is asserting that the location of the linear (or wideband) O2 sensor is such that it can use just one sensor to monitor the mixture in all 3 cylinders. I would agree that the location in the exhaust manifold where gas from all 3 cylinders passes by would allow this to be done, but I had not realized that O2 sensors were now fast enough to make this practical.
To make the arithmetic easier, we could assume a low speed cruise rpm of 3600rpm which gives us 60 crankshaft revolutions/second, which is 30 camshaft revs/sec, and 90 exhaust pulses/sec. This would imply about 11mS of time between exhaust pulses (and about half of this at max rpm).
I went looking for the response time of linear O2 sensors, and so far have not found any ( a little disappointing). I did read the data sheet for the Bosch LSU4.9, and didn't see frequency response there. I have seen aftermarket tuner information on this sensor suggesting a response time of 10mS, but I don't really consider this as reliable. I would expect that if the ECU and linear sensor were working in this way, then it would need a response time of around 1mS.
Now for all I know, foama may work professionally in engine calibration and is exactly correct ion this point, so let's just say I'm surprised.
If the ECM were monitoring the AFR in all 3 cylinders, would the ECU not maintain a fuel trim table for all cylinders? Although I suppose it might well not be able to report out of trim codes for more than 1 "bank" via OBD2.
Can you post more information, foama?
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View my fuel log 2014 Mirage ES 1.2 manual: 46.0 mpg (US) ... 19.5 km/L ... 5.1 L/100 km ... 55.2 mpg (Imp)