It affects the pressure because the tank is none dry. You cant have more than 1.4L of gas on the right side and 0 on the left. Anything over 1.4 on the right spills to the left.

With the right side pegged to max you'll get about 1/3 tank on the needle but as left drops to zero you get no indication of empty tank until the engine stalls.

There might be six oz of gas at the foot of the pump to get just enough to get the engine to catch once and and stall.

It's possible a different faikure has happened but I had the exact symptoms you describe but from the left sender sending too high of a reading. You will most likely see a bone dry tank when you open the port. No reason to open the left side if you put some gas in and the test six shows left reading.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)