johnny: "you're best bet is probably 80% throttle in top gear. Much more than that, you'll be in open loop mode (rich)."
Which brings me to a related question which might be material for yet another thread.
I recently started using a DMM to get a better understanding of how lean-burn works on my VX. I had started with the assumption that there's a certain throttle opening (say, 80%) where there's a fairly abrupt transition to open-loop, and then a lot of extra fuel gets used.
But reading the DMM, it doesn't look that way. AFR is quite lean (i.e., lean-burn mode), even at, say, 50 mph, if I'm very gentle with the throttle. But I usually avoid that, because I've come to believe that a large throttle setting gives me better efficiency than a low setting, despite the advantage of lean-burn. (Sometimes, like in traffic, this means I apply a large setting, but for a short period of time. In other words, my P&G waveform has a fairly high frequency. This can be a lot of work, but I'm finding it pays off.)
But what's interesting is that the AFR response seems linear, even at WOT. In other words, as I move from 80% throttle to WOT, I see the AFR getting richer, but in a gradual, moderate way. There's no sudden transition.
I see the same thing when I use the DMM (dwell feature) to monitor my injectors. As I go from 80% throttle to WOT (let's say in top gear, at low RPM), the injectors continue to open, but in a gradual, moderate, linear way. And even at WOT, they don't open very far, in those conditions. I can only get them to open far if I combine WOT with high RPM.
Anyway, I wonder if a wideband-sensor system like the VX doesn't go into true open-loop in the same way we see with simple O2 sensors, which essentially act more like a switch. My understanding of open-loop is that the ECU starts ignoring the O2 sensor, and uses a stored map instead, because the sensor is no longer providing useful information, because the mixture has moved outside of the narrow range the sensor is capable of reading.
In a way, my question is this. If you're using a wideband O2 sensor, how can you tell whether you're in open-loop or closed-loop mode? With a conventional low-resolution sensor, you can tell this way: "Closed loop operation is indicated by the sensor showing several cross counts per second." (From here:
http://mr2.com/TEXT/O2_Sensor.html; the term "cross counts" is explained there.) But wideband sensors behave in a fundamentally different way, and aren't constantly oscillating (creating cross counts).
So I'm wondering how to monitor open-loop mode on a wideband engine like the VX, and I'm wondering if maybe open-loop simply doesn't happen. And I'm thinking about switching from 80% throttle to WOT, as part of my P&G routine.
This is fairly radical; I've never seen anyone, anywhere, advocate frequent WOT as part of any FE strategy. But I'm considering WOT virtually 100% of the time (except when the throttle is closed). In other words, I might start treating the throttle as a switch (this applies mostly to top-gear operation). So I'm very interested in comments.