STFT... "switching", then nada?

budwich

Original poster
Member
Jun 16, 2013
2,027
kanata
Well, normally when I travel with the traveler in tow (tranny in 3rd), I am monitoring things with torque app as I know I am up near vehicle limits (ie. GCVW). Anyways, last time out, I was watching STFT. Basically, "normally", I would see it "switching" / moving back and forth to various values, some plus, some negative, some more plus, some less, soon. I would think that this is response to O2 sensor switching. LTFT is stable.... typically around 2.8-3.5 or so.
Anyways, I noticed last time at some points in the journey that the STFT stayed basically locked at zero for a long period, which I thought was strange. This trip out, I paid a bit more attention to the response. I could easily make the STFT stay at "0.0" for minutes by keeping even throttle above about 40%. If the throttle dropped below 40, STFT would start "switching" again.
Basically, under normal highway load (doing 100-110 kph) as along as there no "dramatic change" in throttle, STFT would go into this "lock mode" and sit at "0.0"

To me this is very strange, but maybe I don't understand what it means or if it means anything. If my O2 sensor wasn't switching, then there would be a code for "non-switching"... there is no code. Further, if I am not pulling a trailer and I am not able to readily cause the same response... mostly because, I would head past the speed limit.

Anyone got any insight as to what to expect. Is this some sort of "power/open throttle characteristic / compensation"? I can't see how this can be good for maintaining proper fuel / air ratios and ultimately cat "sanity". Its almost like a "carburator flat spot" condition... :smile:
 

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