[97Cavalier]

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.

Thanks,

Jeff

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