so...back to the fuel pump problem. I checked for power at the harness at the tank. There is dark blue wire, a green w/red stripe wire and a black wire. I took a multi tester, set it to 20 volts and grounded the black to the frame and when I test the wires, I get 0 volts at the black, 0 volts at the green and 5.2 volts at the blue with the key on. (not running) I replaced the pump,relay,pressure reg.and filter. I also checked fuses in the pdc. The pump will not energize for sometimes an hour when its cold. In the summer the pump will energize after only a few minuites. Once the engine starts, it runs fine. The other night I let it sit all night with the key in the on position. Pump never came on at all. Any suggestions. 1991 jeep cherokee. 4.0 Auto trans. 4 wd Additionally when we had a warm spell, I went out to try it and after an hour it energized and started fine.

 

Check your grounds, there is one from the body to the rear of the engine head, also there is one on the passenger side of the engine next to the distributor.

try swaping out Auto shutdown relay