Fuel Pump Whining

[azstang]

My wife's 2000 5.0 with 200,000 miles has a really loud fuel pump whine that is driving her nuts. Bosch pump, strainer, and filter installed two years and 11,000 miles ago. Has been whining loudly for at least six months now. Fuel level in the tank makes no difference.

• I disconnected the fuel line at the frame on the driver's side of the engine and ran a hose from the output into a fuel can. With the fuel pump commanded on manually, it sounds normal with minimal whine.
• Connected a fuel pressure gage at the fuel rail and it reading 50 psi. Again with the fuel pump commanded on manually and the engine not running.
• Removed the fuel pressure gage but left the hose connected to the fuel rail. Ran the output of the hose into a fuel can, commanded the fuel pump on manually again, and the pump still whines loudly.

Anyone have any ideas?

 

[J_C]

I'm unaware of anything else to try, I mean if not a filter blockage then all that remains is replace the pump? You could measure that the wiring is getting 12V-14.(n)V to it during operation but besides that?....... besides, low voltage should result in low pressure but not noise.

If it sounded okay when initially installed, and the filter isn't clogged, what else is left besides pump premature wear or strainer clogging?

 

[azstang]

A loud fuel pump could be caused by a restriction in the line somewhere or a plugged filter for example. Loud sound is a sign the pump may be working harder than it should. I spent some time in the service manual today and Ford calls this a Mechanical Returnless fuel system in the Explorer. Meaning there is no fuel returned to the tank and the fuel pressure regulator is in the tank.

The test where I ran the pump with the fuel line disconnected near the engine and the loud pump sound went away shows there is nothing in line from the tank to the engine that is causing the pump to work harder. Like a plugged fuel filter or line.

Then the normal reading of 50 psi at the fuel rail shows the fuel pressure regulator is working. If that had failed and was causing an overpressure condition, and the pump to work harder, I would see it on the gauge.

Seems like it might just be the pump. I'll see if Bosch has a tech line I can reach out to.