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I stand corrected. The R18 DOES cut off fuel completely under certain conditions to improve gas mileage. Here's why the old SGII never showed 9999 MPG, and the one flashed with XGage does. This is the complete response from Tech Support at ScanGauge:
Modern fuel injected engines use a neat trick to save fuel. If the vehicle is in gear and coasting (foot off the throttle) under certain conditions it will turn off the injectors. When this happens, the MPG goes to 9999 (the largest number the ScanGaugeII can display) for MPG and the GPH goes to 0.00.
On some vehicles, the older program could not detect when this happened. The fuel injection would keep computing the fuel it would be injecting if it were not in fuel cutoff and report it to the ScanGaugeII. Starting with version 3.10, we added more checking for this condition. This is why you didn't see it before the upgrade.
I have found on my 01 F150 that I have to turn off the overdrive when coasting downhill to get it into this mode, but then if I turn the overdrive back on, it will stay in fuel cutoff until I step on the throttle or drop below around 40 MPH. This is a neat trick to save fuel. This is why you can actually use less fuel in a modern engine leaving the engine in gear than if you put it in neutral when coasting.
Ron
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