I have a 1998 cherokee with 111,000 miles. I have been experiencing rough idle and less than normal acceleration for some time. I tested the fuel pump pressure at 47psi, needle has a slight quiver at idle but steadies at speed. Tried to test capacity by attaching hose to the pressure test valve on the fuel rail, unattached the fuel injectors so they would not open, unattached the coil wire and than continously cranked the engine to prevent the ASD relay from shutting off the fuel pump for 7 seconds like it said in the service manual. I got 80ml of fuel instead of the 250ml which it said was normal. The only difference was I did not unattach the fuel line to test and I did not use a DRB scantool to keep the fuel pump running as I do not have one. Is this an adequate test and I can assume the fuel pump needs replacing? It is quite an expensive job. Thanks.
Well the fuel pump will only run for 4-5 seconds unless you have the tool to keep it pumping! So your test is inaccurate! Attach a pressure tester and see how fast the pressure falls of after you turn the key back to off.