Fuel pressure for a 91 XJ or YJ 4.0 should be 31 psi with the engine running vacuum hose connected to regulator. With the engine not running or the regulator disconnected the pressure should be 39 psi. that's measured at the test port with the hose connected to the rail. The pump itself should produce at a minimum, 75 psi and may go over 100 psi. The manual says if the flow is blocked the pump should reach 75psi within 2 seconds. Do not run it blocked for over 3 seconds. I doubt if it's just a clogged filter but I guess it's possible. It sure is easier to change a filter than a fuel pump. <img src="/forums/images/graemlins/cheers.gif" alt="" />