Has anyone here use a Dashdyno instead of the Scanguage II? What are the differences. I understand the dashdyno determines fuel usage from mass air flow and commanded air fuel ratio. Is that how scan gauage II does it also? Mostly I am interested if anyone uses one and what they think of it.
never heard of dashdyno but I do know that the scangauge gets it's fuel mileage by air flow, not by actual fuel flow. there is an a adjustment (in percent) for variations so you can tweak it to your actual calculated mileage.
it is basically an error adjustment.
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I'm pretty sure that the ScanGauge and all similar devices don't consider only air flow, but factor in O2 and other easily accessible data.
When using the SG, as you cycle through the available data, some will display immediately while others will cause the display to flash or take a moment before you can see them. I'm almost certain that the ones you see immediately are being used by the SG at all times, while the others are not being used so the SG sends the query only after you select that data (and you have to wait for the data to return).
the AFR is set by the PCM so the scangauge knows that too. I can actually display my AFR on my scangauge (I have it as an X-gauge).
if you know the air flow and the AFR, you can calculate fuel used. that is the way it was explained to me. mine doesn't detect the DFCO thus mine is always going to fluctuate somewhat. I would rather have a gauge that isn't 100% accurate than no gauge at all. not sure you can get one that is much more accurate, it is much more accurate on my wife's element as it actually picks up her DFCO and compensates for that in the calculation.
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The dashdyno, I believe, is like a scan guage II except that it has a datalogger. The reason I am looking at using it is because our new 2008 Chrysler Town & country with 3.8l with 6 speed gets 12.5mpg in city driving. Our previous Chrysler(Plymouth) minivan with 3.3l got 17-18 mpg.
The new van is rpm happy. It will not upshift until 1800 rpms, even with the slightest amount of throttle. If the rpms never exceed 1800 rpms your speed will never exceed 12 mph. Further, upon coast down from 37 mph the rpms go down to 1100 rpms only to jump to 1500 RPMs. It does this a number of times. Never going below 1000rpms until the vehicle is virtually stopped. Any thoughts, besides the stupidity of buying a gas hog, as to whether this is normal operation for a late model vehicle.
That behavior is in line with what general consumers want, plus a little bit of overcompensation (for the minivan image). They're trying to make the minivan exciting by making it accelerate immediately without having to downshift, as well as avoiding harsh downshifts that could jerk the passengers and wear the transmission (do they still suffer from the transmission weakness that early Chrysler minivans did?).
It seems that a large portion of new car buyers not only want the excitement of speed, but actually enjoy engine noise. The example I use to demonstate this the Noise Pipe found on the VW GTI. It is a duct from the turbocharger to the glovebox whose only purpose is to bring noise into the interior; by blocking it off you improve performance slightly.
Being a new 2008 model with a 6 speed transmission, I wouldn't be surprised if it has buttons / paddles / some sort of control meant to encourage you to shift it manually. Can you convince it to shift earlier by using that?
Another strategy to try is to just accelerate harder. Perhaps it's designed to work more efficiently with faster acceleration.
I'd check the EPA ratings on the old and new vans, then take it in for service. Tell them that you are driving the same as you did in the old one and expect X mpg due to the EPA ratings (which are a featured selling point of the vehicle). So, if the 2008 model's rating is 14/18 and the older model's rating was 15/20, you could say you expect 16 from the new one since you got 18 from the old one.
If they try to tell you that 4mpg isn't much to worry about, point out that 4mpg is 1/3 of your current mileage, and maybe do the math that shows that 4mpg costs a lot more money when it's the difference between 12mpg and 16mpg than it does when it's the difference between 30mpg and 34mpg, as such:
400 miles per week scenario
12mpg: 33 gallons
16mpg: 25 gallons -- the 4mpg difference between 12 and 16mpg is 8 gallons
20mpg: 20 gallons
25mpg: 16 gallons
30mpg: 13.3 gallons
34mpg: 11.8 gallons -- the 4mpg difference between 30 and 34mpg is 1.5 gallons
(This is an inherent weakness of using Distance per Volume to measure fuel economy, it doesn't scale accurately.)
When it's all said and done they might not be able to do anything for it, but at least the warranty service will cost Chrysler money and they'll log the data and know better for tweaking next year's model. You may end up having to get a custom tune (not a common pre-fab flash tune) to get better shift patterns.