Removed fuel pump today to discover that the tank is nearly empty (quarter of an inch on the bottom) with the float (or whatever it is called) on the pump is totally dry. But the fuel meter on the cluster shows 1/4 of the tank and the light is off... So, - is it possible that the pump is OK? What would be the best way to test it? I guess, I can apply 12V to it and put it into the jar with water (can I do so?) or gas and see if it pumps.
Another question - for the future - how do I install it back. I tried that so that I don't leave the tank opened and can't push it back. The rubber sealing around the top doesn't seem to allow it back. Any suggestions? Do I just force it or use any tools?
And back to my issue - it is possible that I just ran out of gas, but:
1. Why does it still show fuel in the tank?
2. If the tank is empty and I start the car - should I see normal (35-50 psi) pressure at the engine? Or pump wouldn't run at all?
Thanks!

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BMW X5 2001 3.0