which to believe, scanguage or car readout? - Fuelly Forums

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Old 09-15-2007, 10:01 AM   #1
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which to believe, scanguage or car readout?

so the scan guage typically shows about 4 mpg lower then the car display

this is a surprise to me since they are both gathering the same information to calculate their result

anyway, which is more liklely to be accurate?
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Old 09-15-2007, 10:33 AM   #2
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perris -

The car readout (on your Solstice GXP?) may be using the actual pulse width of the fuel injectors, so I would trust the car display. The ScanGauge allows you to tailor/calibrate the MPG to your car at fillups to reduce error.

I like to say that the ScanGauge is a Jack of all Trades and Master of None. This is not a knock on the ScanGauge. It has to work with the lowest common denominator of data inputs that are available, as provided by the OBDII protocol. For me, I use it as a "relative" barometer of MPG. It teaches you to be a better driver, which is where a huge chunk of your MPG improvements will be coming from over time.

But the best thing to do is see which one is more accurate at gas station fill-up time.

CarloSW2
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Old 09-15-2007, 10:51 AM   #3
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I think the SG gets more accurate as the tank gets lower. For example if you fill up after only using 1/4 of a tank then the SG might be 15-20% off. If you filled up at almost empty then it might only be 1-2% off. I don't think any gauge will ever be 100% accurate due to variances in stations and pumps. Like Carlos said, the SG is good to use to help improve driving.
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Old 09-15-2007, 12:49 PM   #4
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Have you calibrated the scangauge with a full tank of fuel?
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Old 09-15-2007, 01:07 PM   #5
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thanx guys for all the responses

I have not done a calibration, just right out of the box

I did the math result vs the car readout when I first got the gxp and it was incredibly accurate so I guess that's the answer

by the way, how do you calibrate the sg?
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Old 09-15-2007, 05:14 PM   #6
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Quote:
Originally Posted by perris View Post

by the way, how do you calibrate the sg?
When you fill up

I think it's something like

Home --> More --> Fill up.

The SG will say how much fuel has been used. Compare that to your actual consumption (from the pump) and set the fill up number to that. If you make a change you'll see a +/- percentage change --> this is your calibration offset from the default.

It's all in the manual
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Old 09-15-2007, 05:46 PM   #7
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perris, do your speedo calibration as well - use a GPS or time lots of mile marker intervals - 1 minute exactly with a stopwatch at a steady 60 mph.
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Old 09-15-2007, 08:30 PM   #8
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Mine uses a 12.9% adjustment factor after I use a whole tank of fuel. I think you will find that is your problem
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Old 09-17-2007, 07:08 PM   #9
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ok, did all calibrations and scanguage is now reading the same as my disp;ay so thanx for all the help

here's an interesting thing though, when I do the math my dispay was wrong also...the math shows me getting 43 miles to the gallon over a 100 mile trip, the ecu showed about 39

this is because the fill up was in a fraction that the scangauge couldn't get to and I rounded up

anyway, thanx again for all the help

by the way

has anyone used the dashhawk?...it cost double but has more readouts...like fuel mixture...it can display 7 readouts at once and it logs the trip, it also has a data base to read the codes so you don't have to look them up

looks pretty good but this is obviously a better deal if you don't use the performance readouts from dashhawk
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Old 09-17-2007, 07:50 PM   #10
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perris -

Never noticed the dashhawk before. Looks like a Cadillac version of the ScanGauge. The data logging is righteous if you can extend it over a long period of time (aka a normal long commute).

I have always considered getting the CarChip, which is only a data logger. The dashhawk is two in one and delivers (data logging) that the ScanGauge hasn't provided yet.

CarloSW2
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