My 2000 Ford E-350 Super Duty with Triton 5.4 Liter V8 has developed a strange behavior with the fuel pump. The fuel pump will not power up consistently when the ignition key is turned on. I have replaced the fuel pump relay and checked the inertia switch to no avail. Each time the ignition switch is turned on, the fuel pump relay activates for approx. 1-2 seconds but does not always energize the pump. If the pump energizes, the van will start and run. This can happen warm or cold and in order to start the vehicle it usually usually requires the ignition switch to be turned on and off several times before the fuel pump energizes (even though the relay activates each time). Any Suggestions?