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Old 12-15-2011, 04:06 AM   #13
roger 04 rt OP
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Joined: Nov 2011
Location: Massachusetts
Oddometer: 2,272
Originally Posted by Poolside View Post
Ok, you are limiting the term 'Closed Loop'. I'm just trying to slow down the erroneous conclusion rate.

I can't offhand recall the data rate (sweep speed) of the GS-911. Do you know what it is?

On the charts you posted, is the X axis in seconds?

Good questions. And honestly, some of the sampling statistics are at the limit of my "pay grade".

When I use the term Closed Loop, I'm referring to the times when the Motronic ECU is using the O2 Sensor output to create a mixture that oscillates between a slightly richer mixture than 14.7:1 and a slightly leaner mixture. Here is a generic chart of a Closed Loop waveform for those who haven't seen one (I've added the asterisks which I'll come back to in a moment:

The sampling period of the GS-911 varies and had a median time of 0.64 seconds (640 mS) in the Highway Test Ride data set. This is slower than one would like, and it makes interpreting data that changes more rapidly than every few seconds more difficult. However longer term trends such as the shift in and out of Closed Loop mode are easier to see. Averages can also be computed. The key point is that the charts aren't quite like what one would see with an oscilloscope. Here is a chart of sampling times from one run:

So going back to the first chart and looking at the asterisks, you can see that if those were the points that the GS-911 logged, you would not see the full picture. However, if you group all data points taken during Closed Loop times, you could compute the Average Voltage value which I did for the Highway Test Ride data set.

Average Closed Loop Lambda Voltage: 414 mV based on 994 data points taken during all Closed Loop conditions. This is as expected and implies a pure gas Air Fuel Ratio (AFR) of 14.7:1 (approx). This suggests that during closed loop the O2 sensor and ECU are toggling between richer and leaner than 14.7:1 like the generic chart above shows.

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