Volvo: fuel issue, gas gauge, pressure gauge

Question
1990 740 with only an in tank fuel pump...negative wire on in tank pump shorted months ago so I resoldered and it worked great for a while, my gas gauge hasn't been accurate since then,  it registers totally empty when i have 3-5 gal left.  had a lot of trouble putting the sending unit back in and that may have something to do with my new problem...
Now the car will start and run but then die off when  you push the gas or sometimes immediately with no user input  i managed to move it about 1.5 miles by pushing gas pedal in then letting it out repeatedly just in the top inch of the pedals travel range and the car would speed up for a few seconds at a time...i put an inline pressure gauge on between the rail and line and it registers a max of 18-20 psi after being turned off a few minutes it goes down to 10.  The fuel pump used to make a steady short whirring when you turned the key now it has a whir whir whir sound.  Its definately sending a lot of gas to the rail but i have no gas returning to the tank, not enough pressure for the regulator(already swapped with a  good one) maybe? Or could gas be leaking in the tank bringing the pressure down?  don't want to remove sending unit again if at all possible... any help would be great i like to think I know a good deal about this car but this one has me stumped.  

Answer
Hello! The best advice I can give you is to replace the entire sender/fuel pump unit with a new. I have found the tryind to repair them does not work. I would have an experienced Volvo technician do the job for you. You can break the new sender if it is installed wrong.

Jimmy