skewbe -
Quote:
Originally Posted by skewbe
Hey CO, good on ya for testing, but something doesn't add up. No argument that you got 3.6 free miles on the second test in one direction. But the MPG differences might be misleading.
Since you used no fuel on the way down, the climb back up MPG is 1/2 the total MPG. Trip 1 = 23.6 mpg on the climb, Trip 2 = 33.7mpg on the climb.
Given this (and the drag of the engine) it seems apparent that the car stopped where the average return trip is significantly steeper in test 1.
I think you would have to cover the same course/distance (i.e. enable the ignition a couple times on test 1) in order to get an accurate comparison.
Had you slammed on the brakes and turned around at 5.1 miles in test 2, the mpg results would have been identical, the question is how much extra fuel does it take to extend test1 to cover the same ground as test2?
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I agree that covering the same distance would be a
better comparative test, but I don't think the reported MPG would necessarily be the same, at least not for my Saturn.
On the ScanGauge, with my engine off, coasting in Neutral, I still see 0.1 GPH (Gallons Per Hour) consumption. This must be a fudge number to avoid divide-by-zero errors for when the fuel injectors are off. This fudge number leads to *another* silly value I see in the ScanGauge. When the engine is
off, at X MPH, with the key in the
run position, I see X*10 instantaneous MPG, i.e. 39 MPH yields 390 MPG. In this context it should be the "infinity limit" of the SG, or something like 9999 MPG. But 390 MPG now makes sense to me because :
39 MPH / 0.1 GPH = 390 MPG!!!!!
If CO ZX2 covers the same ground (5.1) miles in
less time and his ZX2 talks to the ScanGauge in a similar manner (I can test this, my Dad has a ZX2), the 0.1 GPH will be divided into a smaller portion of time when the downhill MPH is higher and result in greater
total MPG for the Engine-Off-Neutral test. Let's plug in the example numbers, assuming that the 56 MPH average would also apply for the first 5.1 miles (this example would apply for my Saturn in relation to the ScanGauge) :
Engine Off in Gear
36 Miles/Hour for 5.1 Miles => 5.1 / 36 = 0.142 Hours
0.142 Hours * 0.1 GPH => 0.014
Pseudo-Gallons
Engine Off in Neutral
56 Miles/Hour for 5.1 Miles => 5.1 / 56 = 0.091 Hours
0.091 Hours * 0.1 GPH => 0.009
Pseudo-Gallons
The second test over 5.1 miles will yield a higher MPG for the round trip because the Scangauge is fudging the engine off numbers. The ScanGauge, when confronted with the
infinite (MPG), goes a little loopy,
.
This is a defect in the ScanGauge software, *or* a legitimate compromise in a context where the ScanGauge is not designed to operate, depending on your POV.
Tentative Conclusion : If CO ZX2's car is reporting 0.1 GPH in Engine-Off Coasting mode, he is actually getting even
better downhill MPG than he is reporting.
When the engine is off, all bets are off regarding ScanGauge accuracy. Different ECU/PCMs are saying different things to the ScanGauge.
The ScanGauge is good for comparing apples to apples, Saturns to Saturns, Geos to Geos, etc. ad-nauseum ...... It's also good for comparing relative gains of your own car, but the gaslog tells the real truth.
YMW(ill)V!
Orrrrrrrrr, how 'bout them apples!
CarloSW2
Linear Mode
