Can someone explain our fuel tanks please

[voodoomelon]

Hey guys.

Have a 2005 E66 facelift 740Li.

Car wouldn't start few weeks back, in-tank fuel pump was dead so replaced it with an OEM pump.

Issue now though is the right side of the tank (pump side) stays full, until the left side of the tank is completely empty.
Going by what everyone says online, and my mechanics opinion, both sides should empty at a fairly uniform rate, until the left side is empty and then the right side (pump side) fully depletes.

The reason we know it's like this is because we popped open the fuel pump again as it didn't seem to be sealed properly (smell of petrol and small petrol leak).
On opening it, it was full to the brim. Yet the gauge read half full (which was correct).

So to sum up:
- Car runs fine, from indicated full to completely empty.
- Car is displaying correct amount of fuel at all times.
- Car is emptying left side of tank completely, then starts on the right side.
- Smell of fuel constantly in the cabin - was an obvious small leak around the top seal of the pump, perhaps from being overly full for weeks?

At the moment my gauge is reading about 2/5 full.
This is the reading from the secret menu (when sitting stationary with the engine off):



...which quantity-wise is correct. But it's all in the right side of the tank

Strange thing is though when I start driving, the left side starts reading between 5 litres and 11 litres, changing quantity constantly. Come to a stop and it reads zero.

Any thoughts? Thanks!

[DoktorB]

Best thing with a marvel of technology like a 7er is always plug it into the diagnostic. Theres probably a function to look at exactly what fuel level is being measured.

You have 2 level senders on your tank, Maybe one of them is not functioning correctly or the link from one side of the tank to the other is not working.

http://bmwfans.info/parts-catalog/E65/Europe/740i-N62N/feb2007/browse/fuel_supply/fuel_pump_and_fuel_level_sensor/

[voodoomelon]

Will hook up DIS tomorrow and see what it says. Don't recall there being a fuel error though when I was diagnosing the pump though.

The suction link between both sides must be working if it empties the opposite, non pump side first. Just very odd that it empties the pump side afterwards.

A chap in on US forum is adamant its the sender on the left side of the tank, i'm not so sure as the gauge is reading correctly at all times.