Like I said, I'd check the operation of the Exhaust flap on my 1250. Just keep in mind that the 1250 is using a Wideband O2 sensor rather than the Narrowband type used on all previous models. This makes a difference to how much the Ecu relies on feedback fro the sensor, as the WB sensor has a quicker response and a more accurate reading. Additionally, the 1250 has a #3 sensor placed after the Cat. This is a NB sensor.
I have used the GS911 for reading, and I've been recording the
Coolant temperature, RPM, Voltage from the #3 sensor, Flap position and the O2 factor for each cylinder.
The NB sensor, when cold, offers no output. It acts as if it is not there. When warmed up it will offer a reading of 0 - 1 V, where 1 volt is very rich, and low volt is lean. Rich and lean in this contex is richer or leaner than AFR 14,7. The WB sensor works totally different, and it does not offer a direct voltage reading. The signal needs processing before a reading may be made. GS911 does not offer such a readout. The closest we may get out of it is the O2 factor. This is a percentage of extra fuel added to the amount decided by the mapping. The amount decided by mapping, temperature etc is multiplied with this factor, so anything above 1.0 will add fuel, while anything below fuel will subtract fuel compared, and it is based on the O2 sensor feedback.
A couple of lines in the readout offers extremely different values. I think this is a signal error picked up by GS911 and should be ignored.
Ok Here goes:
This is the table while engine is warming up. The first column is the time, recording seconds from start of recording. I have edited the table to show the readings in two main columns, where the second one continues from the first one. check the Time column, and it makes sense.
As you can see, the coolant temperature starts at 55 degrees. That is because I screwed up my first reading, and by then, the engine was a bit warmed up.
What the table does not show is the min and max value of the Flap position. When powering up, the flap is cycled. GS 911 is too slow to pick it up, but the main point is: When the flap hits the Closed mechanical stop it reads 10%, and wide open is somewhere around 57%.
Engine is started around time marker 30 seconds, and we can see that the flap immediately flips open to 52,85%. That is very near full open, which is around 57. At this point, the O2 sensors are cold, and offers no feedback. Hence, the ECU offers a default value of 1,22 and 1,13 for richening the fuel, to be on the safe side.
But already 3 seconds later, the flap goes towards a bit closer, 43,35%. But this is still 2/3 open, and show clearly that my theory that the flap contributes to active affect the fueling does not hold water. We can also see that while the O2 correction factor now is approaching 1, the Lambda voltage from the #3 is still way above 1 (meaning it is still cold, and the higher voltage is probably a bias voltage injected by the ECU, helping to identify a faulty O2 sensor. This is probably what screwed up the AF-XIED back in 2016).
At time marker 44,938 (14 S after engine start) the Lambda voltage falls below 1 showing that the #3 sensor has warmed up. The O2 correction factor is now just slightly above 1.0, meaning that the two WB sensors are also in the loop by now. In fact, if we scroll back, we can see that the O2 correction factor dropped from the default number already 4 seconds after start, while the #3 NB sensor is still warming up.
We also see that now, the Lambda voltage rapidly drops towards 0,2 and below. This indicates that the exhaust leaving the CAT is starved by excessive oxygen, meaning the Cat is doing it's job.
The remaining table shows that the engine is now warming up with a steady 2/3 open flap, the fueling is sharply controlled by feedback from the WB sensors (O2 correction factor), and the cat is working.
Then over to the table for warm engine:
At idle, the flap has now closed slightly more, the cat works, and the mapping needs hardly any correction by the WB O2 sensors.
The interesting part here is that when bringing up the RPM passed 4K, the flap starts to close, and at 6K the flap is fully closed to the stopper (at 10%).
This again points towards all noise and no active emission control.
By now, you got the hang of the numbers, so no further comments may be required from my part.
We may conclude that the flap is controlled actively by the ECU, and noise control seems to be the main target.
This, however does not mean that the closing/opening of the flap does not affect the fueling. It means that the ECU is capable of handling it.
We may also learn that the NB sensor is slower to react than the WB sensor.
Even if the flap is most likely not part of the emission control, it will still affect the fueling.
Back in the days of the carburetor changing the muffler meant re-jetting to compensate. So we know the restriction in the exhaust system affects the power output and fueling. (Why else spend money on de-cating? And de-cating meant the engines would run lean, back in the days before adaptive ECU).
This leads us to conclude that especially when the engine is cold (needing more fuel), if the flap does not match the preprogrammed position, this may affect the pre programmed fueling before the O2 sensors are able to catch up and compensate, meaning the first 10 - 15 seconds after startup for the 1200, while much quicker on the 1250.
And again. This are readings for the 1250, while the thread started out debating the 1200.
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