View Single Post
Old 11-18-2008, 11:39 AM   #16 (permalink)
MetroMPG
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,532

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 54.46 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car Mirage - '14 Mitsubishi Mirage ES (base)
90 day: 62.14 mpg (US)
Thanks: 4,082
Thanked 6,978 Times in 3,613 Posts
Quote:
Originally Posted by Formula413 View Post
As to why the correction factor seems to change, that's a good question. ... Does anyone know exactly how the SGII comes up with it's fuel usage estimate?
Aha! I think your question solved the riddle.

The SG calculates fuel consumption based on air consumption, and extrapolates fuel use with a formula based mostly on stoichiometric air-fuel ratios.

But I've changed my driving style. I used to do a LOT of pulse & glide (P&G), but now I mostly drive with load (DWL). In the Metro, P&G consists of a lot of non-stoichiometric, open loop acceleration. DWL keeps me in closed-loop stoich mode almost all the time.

So, the ScanGauge probably didn't know what the rich burn rate was/is, and obviously it was guessing wrong. It was underestimating it, which is why the offset that worked best when I was doing lots of P&G was +8%.

Also: maybe Linear Logic updated the SG's formula between versions? I've also gone from SG1 to SG2 since I first figured out that +8% offset.

Anyone else upgraded and noticed any difference?

Good reason to use a MPGuino.
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote