First, take a look at pic 1 and confirm I have the correct part you are having trouble with.
As far as reinstalling it, what can happen is the fuel tank, being plastic, can warp or bend from the weight of the fuel. This happens over time making the round opening more like an oval.
Inspect where it screws on to make sure it is round. If it isn't, here is what I suggest:
Loosen the tank mounts (do not remove, just loosen). Take a floor jack and a piece of wood the same width as the tank and place the wood between the tank and the jack. The wood distributes the pressure from the jack. Gently lift the tank. Once the weight is removed, see if you can get the module locking nut to screw on for you. Lifting it will help eliminate the distortion in the tank.
Please keep in mind the tank is plastic, so do not over-pressurize the jack. You don't want to crack or damage the tank.
Let me know if this helps or if you have other questions.
See pic below.
Image (Click to make bigger)
Monday, October 25th, 2021 AT 8:07 PM