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97Cavalier 09-05-2008 01:10 PM

Trouble w/ Scanguage...
This morning I went to the gas station to fillup as is normal for me at the end of the week and, after fillup, the MPG readings on my Scanguage II are off by a good bit.

I keep the booklet with me and, to my knowledge, I reset the guage as directed after a fillup, callibrated the gallons, set the fuel cost and saved the data. The issue that I'm seeing is that my Scanguage II is now showing a 20-30 MPG drop when the other 3 guages that I monitor (RPM, MPH, TPS) show normal readings.

Example 1: At 30 MPH, 9-10 TPS on flat ground with little to no wind, I usually get 105 MPG coasting in neutral with the engine on. This figure can be + or - 5 MPG depending on road surface and other influences. After my fillup this morning I was seeing 70-80 MPG at 30 MPH with 9-10 TPS on flat ground with little to now wind.

Example 2: At highway speeds of 50-60 MPH, 10-12 TPS on flat ground with little to no wind, I usually see 50-55 MPG while holding my speed steady but this morning I was seeing 35-40MPG.

I stopped in a parking lot at one point, shut off the car, unplugged the Scanguage II, sat there for about 10 seconds before plugging it back in and resetting it to the defaults and then resetting the values in it to my car but the MPG readings remained low.

Does anyone have any ideas on why this might happen?

Is there a way to completely wipe out the values in the Scanguage and start over as if it were brand new?

Has it gone belly up on me?

To my knowledge there is no mechanical issue with the car that would cause this performance drop after stopping at the gas station. The speedo and tach in the dash match the Scanguage II readings very closely, i.e. speedo is about .5-1 mph different and the tach might be as much as 400-500 rpm off but this has been the case since installing it.

My mileage traveled always matches when the value on the Scanguage is compared to my trip odo and the normal odo on the car. The car drives the same, there are no idiot lights showing on the dash and it doesn't seem to be running at a higher rpm than normal.

Also, I don't know if this makes a difference but I take the Scanguage out of the car when I get to work and when I get home at night. I don't want it getting too hot during the day and I don't want it stolen at night.

Any help or thoughts on this is appreciated and I hope I can find my purchase receipts for it at the house tonight.



Car Info:
97 Chevy Cavalier LS
2.2L 4 Cylinder
4 Spd Auto
206,500 miles

Brian03cav 09-05-2008 01:34 PM

it sounds like maybe you have been calibrated to a closer correctness. i received my scan gauge after i filled up (friday) so i had to re-fill up and hit done on the gauge, effectively zeroing it out. considering our cars are pretty similar, i see the numbers you are saying you got before now. without the scangauge i measured best of 42 highway, so the numbers i see on there are in the 50s sometimes holding on highway, but i feel like that will go down once calibrated.

everything i read on it says the averages and the instant mpg will become more realistic as you use it. also, keep track using your odometer, that way you can tell if you're still on track.

azraelswrd 09-05-2008 03:05 PM

You can reset the Scangauge using MORE>MORE>MORE>USE DEFAULTS. One thing I've learned is that after the 3rd tank, you might not want to constantly fiddle with the fillup adjustment.

I found out the hard way that it skews results later, so I zeroed it out (after 50mi and 1 gal) and I'm hoping my numbers are more realistic now that I've gone back to my original adjustment factor (12.2%). I knew something was wrong when I released the gas pedal and my instant MPG wasn't dropping as fast as it normally was and cruising at 45mph/17TPS the instant MPG value was much higher than normal (which inflated my trip and tank MPG) even though the GPH appeared normal. Somehow the SG wasn't accurately adjusting for gas usage. MPH, distance traveled and GPH were still accurate.

I'm not sure if removing it while the car is parked would be a factor.

Next time you fill up, record what your car says and what the scangauge says:

SG tank miles
SG tank MPG
SG tank fuel used
car miles traveled
car fuel used

...and plug them into this calibration excel sheet.

CleanMPG Forums

Hopefully those values will produce more accurate results the next time you refuel.

97Cavalier 09-05-2008 06:05 PM

It would certainly be nice if this was just a calibration by the Scanguage to be more accurate but a drop of 20-30mpg just seems like a lot.

Time will tell though and I'm anxious to see what happens at my next fill up.

As for the figures that azrael suggested noting, I'll be sure to copy those down and compare what the Scanguage reports against the trip odo and gallons used at fill up.

Thanks for the replies,


azraelswrd 09-06-2008 04:21 AM

I wish I had taken my own advice now. :D I had to manually adjust my fillup value and it's at 15% now but I still think the numbers are a little too "generous" for what I'm doing. I won't know for sure until I go back to the pump but that won't be for another 2 weeks (ideally). Again, I'm not sure if it was the gas or the tune-up or the tires... too many variables to deal with.

EVDRVR 09-06-2008 10:09 AM

Last summer I made a error in entering the fueling amount and SG II was "whacked" really badly. My guess is you might have done the same.

I only use it in my rental cars so I don't stay real familiar with the calibration portion. Anyhow, I did what seemed intuitive at one stop and ended up having to reset the unit. Can't recall exactly what I did wrong but as they say, "garbage in garbage out." My attempts to correct my entry error only seemed to make it get worse. Reset to the rescue.

I was running the SG II along with the computer in a new Impala. The Impala's computer was awfully good at doing the fuel so my error was quickly pointed out.

BTW hypermiling the GM V6 with cylinder de-activation is pretty easy. Makes for a nice ride. And SG II worked fine. (they have a note that says cylinder deactivation can cause problems with SG, it didn't on the Impala, worked beautifully)


97Cavalier 09-11-2008 03:42 PM

Well, the results are in and my mileage for the tank is down by roughly 120 miles. When I filled up this morning the ScanGuage II did not need any calibration with the amount of fuel added to it. Prior to having trouble I would have about 3%-5% adjustment with each new tank.

Maybe this is the ScanGuage adjusting itself but if so, the tanks that I've had before this have been badly skewed in their readings and I'm disappointed in the mileage readings that I'm getting now.

I realize that 1 full tank with the new readings is not nearly enough for a definitive answer to this issue. I guess this is really a time to practice my hypermiling techniques to see what I've learned and see if I can improve on this reduced mpg.

So my question now is... How do I reset the ScanGuage II to factory presets and wipe out all of the data that I've entered? Is it as simple as calibrating it to a new vehicle and running it on that vehicle for a full tank or is there something else that I need to do?

I've got some other questions for the forum but they'll go in a different section so I don't clutter this post up.

Thank you very much to everyone that replied. I do value your own experiences and will learn as much as I can from this.

Until next time, keep the shiny side up and drive safe,


97Cavalier 09-15-2008 12:35 PM

Friday night, 9/12, the alternator died on the way home from work and I had to have the car towed into the shop.

When I went to work that morning the volt light came on for a short time and then went out so I switched the ScanGuage over to watch volts and the ignition readings. About halfway to work the ABS light came on and wouldn't go off and I could hear a definite whine coming from the general area of the alternator. That evening when I left work, the ABS light was back on within 5 minutes of starting the engine so I stopped at an AutoZone and they were kind enough to check the electrical system for me.

Their testing box registered about 9 volts at idle before the guy drew an electrical load and killed the car. It went zip with the load and pop when it stopped and then we just stood still... and then the car wouldn't start again. He managed to jump start if for me and then all the idiot lights were on and the car wouldn't idle unless I held the rpm north of 2K.

I managed to get halfway home when it finally died out on me and thankfully I was able to get off the freeway and into a gas station with some ultimate EoC. Right now I'm waiting on an estimate for the fix but after talking with my mechanic he's of a mind that this could've been part of the reduced fuel mileage if the computer was trying to cut back on system functions to keep the car going.

I don't know though and we'll see what happens once I get back on the road again.

Thanks again for the knowledge above,


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