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The way I understand it, the SCII reports fuel consumption as a calculation based on air consumption.

If this is true, I may be getting worse mileage while coasting in neutral, than I would if I were to just let off the gas pedal.

How can I tell if my car cuts fuel when coasting (still in gear)?

The SG-II as far as I know does report based on air 'consumption' and doesn't yet understand the state of "ICE spin", where the ICE is turning over but no fuel is being consumed. In this condition (at least with the Prius) the SG-II will report MPG that tracks pretty closely with either 3x or 5x MPH - for example 165 or 275 at 55MPH, 123 or 205 at 41MPH, etc. Contrast to showing 9999 when the ICE is actually off and you are moving.

More oddities occur when you have reset the SG's trip meter and have been taxiing around a parking lot or something without your ICE on at all. The instantaneous will show 9999 all of the time, but if you look at your trip MPG it will show some absurdly high number (2000, for example) but not infinite.

How can I tell if my car cuts fuel when coasting (still in gear)?

I'm not sure if you can tell without using either an instantaneous mpg readout (such as the ScanGauge) or looking up the specs for the car. Fuel cut is a very useful feature but isn't useful in the same places as coasting in neutral. If you need to do some short term slowdown with a ramp back up to speed shortly after, timing it so that fuel cut will give you enough engine braking to get the job done is definitely a plus. If you have more time, though, you could be substantially better off just coasting in neutral for longer. Fuel cut is good but slows the car down quite a bit so you don't get to do it very long. Coasting still uses (a little!) fuel but if you use it correctly you can eliminate the time you would have spent in gear at a higher rpm using even more gas.

In other words, if I have to quickly slow down or I have only a short term need to slow down I'll use fuel cut (my car doesn't have it but the wife's Escape does). If it is a planned stop most of the time I'm better off using a longer coast which reduces my speed much more gradually but keeps the rpms low throughout.

I hope that helps!

As far as I can tell, my Scangauge II doesn't recognize any difference in my Subaru between:
(a) coasting in neutral, ICE ON
(b) decelerating in gear, ICE ON
(c) coasting in neutral, ICE OFF.
The gph reading shows 0.2 gph under all three conditions, even after waiting for a LONG time.
If this 0.2 gph value is what it is using for its AVG MPG calculation, then it doesn't help me distinguish which of the three tactics works best under different scenarios.
Any ideas how to fix this, or do we need a Scangauge III?

I'll have to try that sometime -- I've never kept the gph gauge up for monitoring those activies!

I tend to (as Ken alluded to in the Daily Grind thread) keep the current trip mpg up when I'm driving and I can see a difference in the rate of change among those three. I can also see it IIRC when I've got the instantaneous mpg gauge up.

In fact, I think I'll watch the gph readout today as I'm driving. Ken suggested keeping an eye on the gauges instead of the current trip to see if that made a better dent in my fuel usage on this new route for work.

This was discussed in various prius forums, too. There are a
couple of problems that isn't necessarily SG's fault. One, there's
airflow through the MAF in fuel-cut conditions, so a wrong
assumption could be made if that's the only parameter used in
calculating MPG. Two, and egregiously worse, the Prius ECM and
possibly other cars continues to report a non-zero injector
time after the injectors have stopped firing. The Prius definitely
does this -- it'll hang forever showing 1.2 ms injector time
during a long glide or warp-stealth, which is ridiculous. But
if the SG or other OBD-II device asks, and gets back that answer,
what's it supposed to think? And of course in warp-stealth
you've got positive RPM so you can't base it solely off engine
RPM either. Each hybrid vehicle probably needs some special hack
to determine when you're in fuel-cut at various speed ranges,
and there may not even be one for some cars.
.
The simplest fix would be for manufacturers to report 0 injector
time when that's the case.
.
_H*

.....I think I'll watch the gph readout today as I'm driving. .....

Keep in mind, the gph readout is the Scangauge's estimate of fuel usage, based on the airflow, and NOT based on any actual readings of fuel-flow (if I'm understanding the SGII correctly).

I will try a FAS, and watch the gph, to see what happens.


Hahahahahaha, I wrote FAS. My first hypermile abbreviation use! :Banane37:

Hi, Anon! While you are right it won't be any worse than the mpg readings I'm paying attention to because they are all being calculated from the same data. ;)

I did have a look on the way home and mine correctly shows 0.0gph when I'm in FAS (after the bus reset completes).

Please check your owner's manual before you try a FAS, Anon. Not all vehicles can do this safely. You want to look for the towing directions. If the manual says you can "flat tow" the vehicle (meaning pull it with all 4 wheels on the ground) you can FAS. Anything else and you can't do it safely. A manual transmission is always okay but most AT cars depend on the engine running to pump oil through the gears to keep them lubed as they spin. Roll for any significant distance with the engine off in one of these cars and you risk severe damage to the transmission. Not a cool thing. :(

When I tried it in the loaner Sonata I only rolled a total of about 6 feet.

I forgot to check decelerating in gear (using engine braking) but you could definitely tell the engine had just started after a bump start or key start because gph were stuck at 0.5 for a fair bit. I've also got a strange anomaly when I FAS -- just as the bus reset finishes it spikes up to 1.7gph before settling down to 0.0??? I could see it in the current trip before this as it tends to hold steady or climb during the bus reset, then it dips before coming back up. Crazy!!

:When I got my SG loaded with the beta firmware, I mentioned to Ron that the FEH and the Prius both have PIDs that indicate fuel cut. He was interested, but reminded me of the generic nature of the SG and how difficult it would be to figure out where the fuel cut PID is for all vehicles. I think he is still working on using the loop status and other things to determine fuel cut.

Using the new Cost Per Mile feature, it cost me $0.47 of gas to get to work this morning.:)

Using the new Cost Per Mile feature, it cost me $0.47 of gas to get to work this morning :)

___Carl, that feature is just plain sick :D

___Good Luck

___Wayne

Is this "new feature" just firmware?

Will I be kicking myself for buying a Scangauge last week?