I had a digital/LED A/F Ratio gauge on my turbo Evolution. Frankly, it was a waste of money -- it basically read the oxygen sensor readings and blinked wildly back and forth in normal driving.
The only time it was of use was during WOT runs -- it would show how rich or lean the mix would get when the turbo spooled-up, and it would pretty much hold steady in the green. If it was yellow (or red), then a potentially dangerous lean condition was present. That never happened and it was basically there for looks to fill a 3-gauge cluster of analogue oil temp and pressure. On that car, at WOT you had to watch where you were going because 60 MPH came up under 5-seconds if you did it right - not a silly gauge.
The SG's functions are much more useful.
I'll probably use my digital A/F gauge with an EFIE and a post-cat high temp sensor to make sure my (future) lean-burn doesn't go into lean-engine-meltdown.
But I agree that, especially with narrow band sensors, the value will be fluctuating all over the place, so it's usefullness will be iffy.
I think A/F is much more usefull as a datapoint in a logger so that you can see if your overall lean-burn strategy is working as intended.
There can be FE benefits to having a lambda sensor : I have a wideband + display fitted to my car (although the ECU doesn't use any lambda input), and it has helped to improve my fuel economy greatly. Yesterday I did a lot of driving, at above highway speeds, with no drafting, heavy winds + very heavy rain +standing water. The only fuel-economy orientated thing I did was to ensure the engine didn't go into enrichment mode, but ran at near stoichometric (by watching the Air-Fuel Ratio gauge. Slight increases in throttle caused the mixture to go from 14.8 -> 10.8 with very little increase in performance (but a lot more fuel being used).
On this run, I got 31mpg, while for this kind of driving in the past, before the AFR gauge, I got 24mpg, and that was with better weather conditions too!.
__________________ Team GasMisers5 - #1 for first three rounds of the original GS Fuel Economy Challenge
Miles displaced by e-bike since 1 Jan 2008: 62.6 (0 kWh used)
Just thinking that the O2 sensor is probably a variable resistor and it gets polled by the ECU which results in the irratic reading when being monitored with another instrument. The ECU would only have to apply power to it when it takes a reading. I also wonder if a NA (normally asperated) engine would have A/F ratio swings that big like that of a turbo that has to go rich to prevent detonation.
Now that I've caught up with the acromym meaning, I can forget all about them. Diesels have no O2 sensors, They run from about 100:1 to stoichometric so are perpetually 'lean'. This means that they are always pushing the limit of legal NOx production, but the eff'ing O2 sensor signal modifiers being discussed here will do that, too.
And the bunny has only one pancake on its head. It's that pancake which has another pancake on top, but the bunny has only one.