Fuel Guage Showed 1/4--only took 8.9 to fill?

[ccjazz]

I am planning a 600 mile road trip soon and installed the Road Trip app on my iphone so I'll be able to plan my fuel stops (trip is through the Rocky Mtns) and monitor fuel consumption.

I've been suspicious of my fuel guage for a while but because most of my trips have been in the city with lots of fuel options I haven't worried too much and just topped off the fuel regularly. Well today, my guage was showing 1/4 tank so I decided to use my Road Trip app and start logging. I pumped slowly until it shut off and the quantity pumped showed 33.6 liters / 8.9 US gallons and the fuel guage now showed full. So it seems that my fuel guage is not accounting for approximately half a tank of fuel even though it travels from showing 'full' to '1/4' tank.

Next step was the search function here which revealed a couple of possibilities. Because the needle appears to travel properly, I'm kinda ruling out a sensor that's getting fouled by an obstruction in the tank. It seems as though I likely need to have the guage recalibrated which I read is a "at the dealer only" fix.

My battery did go dead on me a couple of years ago while in winter hibernation (tender got unplugged somehow) and I replaced it. So I'm guessing I lost the fuel guage sending settings.

Any thoughts are appreciated. Am I stuck paying the Porsche 'Premium' at the dealership to re-calibrate? If so I guess I'll have to get out and burn off this tank of gas as low as I dare to.

Holiday here but I'll be checking with my indy on Monday to see if he has the PIWIS but I don't think he does.