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I had noticed that my ScanGauge II shows 0.2gph in my 2003 Subaru Outback MT even when coasting NICE-OFF (it also shows 0.2 gph when coasting NICE-ON). But I was never sure whether this affected the Average MPG figures.

I contacted ScanGauge and was told that the Subaru ECM might be holding the 0.2gph figure when the engine was off, but wasn't given a workaround.

Yesterday I had to stop several minutes at the steam train crossing in town, so I shut down the ICE and sat there ICE-OFF with the ignition on. When I started up again I noticed that the Avg MPG was horribly low, <10mpg.

So today I did a test. I drove 2.3 miles, at which point the Avg MPG reading was 22.1, stopped, keyed off the ICE, turned the ignition back on, and sat there for several minutes ICE-OFF without moving. Here are my Avg MPG figures:

0 min 22.1
1 min 21.3
2 min 20.6
3 min 19.8

The fuel consumption reading showed 0.2gph throughout.

This means the ScanGauge can't distinguish between idle and ICE-OFF in my Subaru, so I can't see whether it is helpful to coast NICE-OFF or to go ICE-OFF at lights, etc.

Any suggestions on how to work around this? Would the new firmware help?

I think the new SG with X-gauge features has a 'cutoff' setting, and you can reset the cutoff to what you want. Anyways, anything under the cutoff is read as 0 fuel useage. I'm not sure on the specifics as I don't have the x-gauge features on mine. Hopefully someone here can clarify.

Try switching to the hybrid option in the scangauge... that might fix it.

Mine (SG I) functions very similar with the exception that it shows only 0.1 gph.

Doesn't do this on my Element, must be vehicle specific?

I think the new SG with X-gauge features has a 'cutoff' setting, and you can reset the cutoff to what you want. Anyways, anything under the cutoff is read as 0 fuel useage. I'm not sure on the specifics as I don't have the x-gauge features on mine. Hopefully someone here can clarify.
Thought about it some more, and this would make sense. The SG could tell from rpm (which it measures as well) whether the ICE is running or not. If the rpm drops below a certain value (or to zero) the SG should set gph to zero for its averaging function just to avoid cases like this where the ECM apparently retains a minimum value like 0.2 or 0.1 gph in memory??

I've got the same problem with my 2003 Impreza when FASing.

Also though sometimes when I'm accelerating and light on the pedal the instant mpg shoots up to 9999. So I don't even know if messing around with that fuel cutoff setting would do me any good. Seems like lowering it would give me accurate mpg's while accelerating, and raising it would give me accurate numbers while FASing, but I can't do both.