Big letdown this tank

[brick]

I filled up this morning in anticipation of my weekend driving. The ScanGauge was reporting what could have been a PR tank of 42.0mpg, but the pump said "DENIED!" 552mi/13.650gal = 40.44mpg. It's still a decent tank but I was expecting a whole lot more!

So what happened? Well, I think it has to do with the SG not quite keeping up with all of the FAS I've been doing. This thing has always overreported fuel consumption slightly, but I've noticed that it has done it a little less so as my technique has gotten more aggressive. I guess this on-off-on-off commute has finally caused it to reach the cross-over point where I really need to dial back the correction factor. Oh, well.

Now, the real question is, what is the root cause of the discrepancy? Either my trip meter is missing ~21mi of distance travelled, or else I tossed a half gallon of fuel out the window. (Or somethign was wrong with that pump, but I doubt it.) One possibility that I don't think the ScanGauge would be able to compensate for is the large number of key starts that I've done. I don't know for sure, but I would bet that they are operating at a very high duty cycle during start-up. It doesn't make a big difference when you do it once every 25 miles, but when you do it...well...constantly, it stands to reason that all of those long pulses would add up. To half a gallon over two weeks, maybe?

Mind you, I'm really not complaining! I'm happy to be over 40mpg when the EPA thinks I should be getting 25-28mpg in this driving cycle. But it would be really great to figure out what's going on so that I can do something about it.

[psyshack]

Strange

Ive never been that much off and I FAS more than the normal Joe. Most Ive seen is about .3 of a mpg, maybe a .4. Strange indeed. I always lag and post the hand calc's.

[brick]

I think I know what happened, and posted a thread in Fuel Economy.