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Old 04-29-2011, 03:33 PM   #4 (permalink)
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Originally Posted by UFO
Either the problem is the fuel consumption calculation at idle is too low, or the fuel consumption under acceleration is calculated too high
If your real tank was LOWER than your calculated one, it could be that the opposite the case - idle may be too high and acceleration calculated as too low ?

Do you have a link for the 0.1GPH idle figure ? I have a 1.9 TDI and mine is measuring 0.12-0.14 GPH - I have configured it as a 1.4 and adjusted 50% of the difference on each tank - my last one was 1.5% out. I have not yet had a 100% exact match but I accept anything under 3% as being inside a margin of error - things like temp when filling up, slope of the car, my ability to 'vent' enough and so on. Plus my tank to tank is not consistent driving - speed, temp and so on. It can't be as a tank for me lasts 3-5 weeks.

I mainly use the SG2 figure to monitor instant MPG - e.g. keeping my instant MPG above my average, as well as other figures such as coolant (grill blocked), MAP and so on.

As for P&G I didn't notice much of a difference in using vs not on my TDI - the difference was within my 3% difference and on one tank better and on one worse for P&G than a non-P&G tank. My tanks last too long to experiment with different speeds really, I could get better results if I did more miles.

My best result has been with cutting out idle whenever I can. I have, for example, switched one part of my route to actually go for a portion which is stop-start vs crawl - I can stop the engine in the stop part but not in the crawl. My last tank gained 8% on this change.

Mine is a manual but I would think that at a stop light you engine is not only idling but also pushing against the torque converter and so your idle GPH I would think is higher.
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