How difficult is it to change the fuel pump in a Grand Cherokee 98?

You will have to drop the fuel tank to gain access to the fuel pump. Use a floor jack to support the fuel tank. Hopefully it is empty. If not fill someone else's tank up with your fuel. You will first have to disconnect the rubber hoses that go to the filler neck. There will be two. Then undo the two straps that support the fuel tank. Carefully lower the tank to get access to the electrical connections for the gauge and the fuel pump. Disconnect them. There will be a couple of fuel line you need to disconnect now also. You have to push two tangs in towards the fuel line and gently pull the connection apart. Then lower the tank and remove from under the vehicle to remove the screw on cap that holds the fuel pump and sending unit in the tank. Once the cap is removed gently lift up and tilt the assembly so you can clear the float out the top without bending the arm attached to the float. The fuel pump is in the center of the assembly. A very pricey item. Expect to pay from 160.00 to 230.00 for the pump. Two other things before you start this project to check. Check the fuel pump relay in the power distribution box in the engine area. If it is bad replace it before going any further. Also on the fuel rail is a cap that you need to remove to bleed off the fuel pressure in the system. It looks like a typical valve stem inside that you would see if you put air into your tire. Beware- pressure runs around 40 PSI. Protect your eyes and if you smoke -don't do so while you work on this system. Good luck. I hope this gets you where you need to get started.