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Old 06-16-2007, 05:45 PM   #1
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Scan Gauge 2 How it works

Can someone explain to me how the SG2 works. I'm electronically inclined so a technical explanation is ok also a watered down version wouldn't be bad either. I know the SG2 gets it's info from the OBD2 computer which get's it's info from the various sensors. But how does it calculate MPG and gallons to empty, etc... Thanks for the help
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Old 06-16-2007, 06:11 PM   #2
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Can someone explain to me how the SG2 works. I'm electronically inclined so a technical explanation is ok also a watered down version wouldn't be bad either. I know the SG2 gets it's info from the OBD2 computer which get's it's info from the various sensors. But how does it calculate MPG and gallons to empty, etc... Thanks for the help
The SG doesn't actually measure fuel used to calculate mpg. It calculates mpg by taking engine size and an assumed 14.7:1 air-fuel ratio and measures the air used. On my SG1, I used to tweak the mpg readout by adjusting the engine size if the SG's mpg was different from the calculated. This is partly why an SG doesn't work on Honda's with lean-burn mode such as the VX or Insight or HCH I with a 5-MT.
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Old 06-16-2007, 06:16 PM   #3
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I thought that EVERY car went away from a stoichiometric ratio (to a leaner ratio) at certain low load conditions. Is that not true?
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Old 06-16-2007, 06:27 PM   #4
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The ECU will always try for 14.7:1 even though the engine may want/need something different.
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Old 06-16-2007, 06:37 PM   #5
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diesels can lean out a lot more.
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Old 06-16-2007, 07:05 PM   #6
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I thought it read the injector pulse width from the ECU and calculated fuel usage from that.
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Old 06-16-2007, 07:59 PM   #7
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maybe this will help...

http://www.scangauge.com/support/pdfs/SGIIManual.pdf
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Old 06-17-2007, 01:36 AM   #8
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Hello -

One thing I have noticed with other OBDII readers (like the CarChip) is that they also only monitor 4 values at once. This leads me to believe that the OBDII "bus" can only place 4 "instant readout" values on the bus at one time.

No proof, just observation.

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Old 06-17-2007, 05:43 AM   #9
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Hello -

One thing I have noticed with other OBDII readers (like the CarChip) is that they also only monitor 4 values at once. This leads me to believe that the OBDII "bus" can only place 4 "instant readout" values on the bus at one time.

No proof, just observation.

CarloSW2
A cool upgrade to the SG2's firmware would be the option of it automatically cycling through user-selected gauges, just like some digital watches allow for auto-cycling between date and time. That would save FE nerds like me from constantly cycling between the gauges and trip data screens.
Shouldn't be too hard for the wizards at Linear Logic.

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Old 06-17-2007, 05:54 AM   #10
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The ECU will always try for 14.7:1 even though the engine may want/need something different.
Reeealy. Wow. I was positive that all cars went a little leaner at low loads in order to bump up FE. Thanks.
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