Hants, what does it read mpg wise when you're idling at a stop? should be zero to make sense, or is it 9999 as well?
back to the basics: the thing is that for this to work, it has to know that there is a reverse load on the engine. Simplest way to know that would be RPM greater than nominal idle with throttle closed...?
interesting, read someplace that some manufacturers did away with the cutoff feature upon introduction of OBDII.... no idea if true...
and here is a vid of the scangaugeII reportedly showing 0 consumption when coasting in gear (not a LC, a CIVIC):
YouTube - Fuel injection shut-off while coasting in gear
and interestingly, the SgII does show a finite consumption and zero speed when stopped and idling... more instructive to show gph than mpg for this...
here's another thought: if you were to coast down in gear and record the speed or gph and rpm (unfortunately the current SGII can not do that, I'm told), and if the injection is indeed cut off at high rpm (yet to be confirmed), you'd probably be able to tell at what rpm it comes back on by looking at the data (either a reduction in deceleration rate or the gph going back up)
still more: just read that there is a "cutoff" function on the scangauge. Called to clarify what that does. Apparently, there is a bit in the ECM that tells whether you are either in injection cutoff mode or under high acceleration (could be either one depending on circumstances). So they ask you to set a threshold for the TPS so that the Sg2 can tell whether the engine is under actual cutoff and display same as zero consumption. Strangely, the ECM will still report a hypothetical injection rate, fuel mixture etc even though the injectors are cut off. A bit murky and room for errors, there...