Re: 2004 jeep grand cherokee
And was it a new assy?
I can't believe that a different assy (new or used) would give the same failure.
I would start measuring voltage to be sure that the problem is not electrical feed related. Then check the ground path for the fuel pump. Can only not explain why the pump would go on for 3 secs and then off for 15.
So first check if the fuel pump relay is not switching the pump on/off, you can feel it clicking when it switches.