In my hast to respond in my last post, I missed this post. I think the below is a good starting point to dig deeper into this:
You want to use a Broad Band and believe it as accurate, that's fine but at least let people see the facts about how the manufacture of the sensor tells you to use them properly. It would really be nice if there was just one of the aftermarket company's that did use them as they were told by the manufacture of the sensor!
My belief in the sensors being accurate is probably different than yours, so I will state my opinion as accurate and then you can state yours and we will see where we differ. In my opinion the broad band sensors are plenty accurate enough to make informed decisions (and I am viewing the narrow bands in the same way). I really do lump AFR tuning in the category of horseshoes and hand grenades, so as long as the accuracy of the sensors fall with in the allowable variance of my target then the accuracy is fine for the application. If I were doing scientific studies and writing peer reviewed technical papers, then perhaps I would agree that the sensors were not accurate.
Attached is a graph of how the absolute pressure in the exhaust pipe effects the output of the sensor at ONE fixed altitude, it changes as the altitude and temperature does too.
So, based on the above statement that absolute pressure in the pipe can cause a variance in reported data is that how you are viewing this? If so, how do you explain FLTRI’s previous comments that a tail pipe sniffer will read fairly linear to that exact same sensor being placed inside the pipe? Wouldn’t the variance in pressure in the pipe alter the readings compared to the more stable pressure of the vacuum drawn sample?
Since you only reference pressure concerns with broad bands, can we assume that you do not have these same concerns with narrow bands? If so, how do you explain how data between narrow band sensors and broad band sensors, both located in the same pipe, appear to follow similar trends in reported values?
How do you explain that the reported broad band sensor values from sensors placed in the pipes are reporting the same afr values as the target while narrow band tuning? Here's a shot of the dyno monitor while I was tuning closed loop last year using a Power Vision:
The reported afr swung no more than +/- .2 afr from my targeted closed loop desired value, and that variance could have easily been just based on the ecm’s attempt at correction in closed loop.
Now if any of the aftermarket companies would use the corrections as Bosch requires you to do, it would not matter but you would need to install and absolute pressure gauge and temperature probe in the exhaust at the time the samples were being taken so the Bosch supplied corrections can be used. If you look at the 13.23 AFR data line it can and does vary from 13.59 to 13.04 just in this pressure range and that is at one fixed altitude and NO correction for temperature is applied yet! So at best you can say is you’re somewhere in that range but god only knows where unless you follow what the manufacture tells you to do.
so, let’s take your numbers at face value. Why should I be at all concerned with a possible reported variation of around a ¼ of an afr value when best power can easily be reached with a allowable range of 1afr? Is the engine going to respond differently at 13.6 compared to 13? I thought the bases of Bob’s little experiment with narrow band sensors was based on this same premise. So why is it good for the goose but not for the gander?
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Topic: O2 Sensor Output (mv) compared to measured AFR (Read 154107 times)