XJ8 Jag 1999 Gas tank problem

check your fuel vents, sounds like its plugged up

Try slowing down how fast you pump the fuel in, the curve of the tank filler pipe and the stopper valve at the end of the pipe(in the tank)will act as a restriction causing a backup when filling too fast. Or the stopper valve is sticking in the tank. To fix that ,you would have to replace the tank.

This problem is caused by the fuel level sensor inside the gas tank, you will need to drop the fuel tank out or remove the pickup bed to access the level sensor which is part of the fuel pump module on most GM products. The part is about $200.00 and 3 hours to install. See picture below. You can buy the part at a very good price from the on line company I use for parts www.rockauto.com

Your description indicates that you may have an issue with the canister vent purge/sol. It is not an uncommon issue.

Chrysler and Dodge have a fuel vapor filter that allows air out of the gas tank but filters the harmful fumes. Usually the problem happens from topping off your gas after the gas pump stops due to the automatic shut off and then putting more gas in the tank (to make the bill an even $50. or to the next $5 increment, or pumping more in just because it fits). Anyway the filter gets saturated with gas, is not able to breath, and causes a vacuum in the tank. Because of this, the anti-siphon ball is not able to float around and sits at the opening of the fuel fill tube and won't allow any more gas to be put in (acts like the car is full). If you pump super duper slow like put a nickel to hold the gas pump handle, it will trickle in without a problem, but it takes forever! Solution, get the filter replaced and don't over fill the tank.

add two cans of Heat gas treatment to it with a full tank of gas to eliminate the moister that is left in the fuel system

If the nozzle is actually hitting something, then there's a problem. There shouldn't be anything interferring with the insertion of the nozzel.

I also have a 04 with a 1.8L. same problem. I took the fuel regulator off. It is a black box behind the rear tire under car. It only has 2 bolts to take off. After that there is a couple of vent hoses from the tank going to this box. Unplug them and 1 electrical connection. The electrical connection and one vent is connected to a T connection on the box that you can unplug by twisting on the T. Take that T off and look inside where you unplugged the hose on this T. There is a spring and a little plunger inside this tube. The plunger gets stuck. I took a little screw driver and some PB blaster and worked that plunger back and forth a couple dozen times and it unfroze. Put it back together gassed up just fine. I did not look but I was told regulator can be replaced for 200$. But a can of blaster is cheaper.

It is a common problem. It is a faulty in tank sender. You can just replace the sending unit by removing tank.

Sounds like the fuel sending unit is bad, which is in the gas tank, along with the fuel pump.