[UFO]

I am sure the reason why the SG does not report well on diesels is it uses similar algorithms that work well for gassers, that is fuel consumption based on air flow. That works reasonably well under load, where the computer will fuel up to the available air, but it falls apart at lighter loads and idle (coasting) because the computer will allow fuel ratios higher than even 20:1. So you calibrate the unit based on average fuel consumption, and you change your route or your driving style with a different mix of heavy and light loads, and your mileage calculations will be significantly off.

I calibrated my SG to my normal commute with the EGR disabled, and my driving technique is fairly consistent. Then I take a road trip. If it is along the front range, with few elevation changes and higher average speeds, my mileage will be slightly higher than SG calculations. If it is through the mountains, the SG calculations will far exceed the actual mileage.

My commuting mileage is about 45-46 mpg. A front range trip will get me about 40-42 mpg, and SG reports 39-41. A trip into the mountains will get me 50-53 mpg, but I've had the SG report upwards of 60 mpg.