Whats this noise

[js250]

when i turn my truck on it makes this humming noise for like 15 seconds i would say sounds like a fuel pump but i really dont know. it only does it mow and then so anything would help its 1999 f250 7.3

[huntnut]

Vacum pump under the hood on the passanger side firewall.

[Goose]

fuel pump i believe i hear it to every morn normal I HOPE

[melmount]

whats the vacuume pump for? does it turn on with the key on? have to be running?

[huntnut]

I think the vacum pump is for the A/C,heater and the 4x4 lockout controls controls and yes it coms on when you turn the key on.

[dalton1]

x2 for the vacuum pump, my truck dose the same thing.

[melmount]

wheres the hose run? does any part of it run any where near the fuel bowl? I am not trying to hijack this thread but i said in my other post that i hear an occasional air leak. I have been thinking its air getting pushed out of the fuel system somehow near the filter? I wonder if it could be from this? I know some seals are bad on pass side front axel? Hows vacuume get to this stuff?

[Highbeam]

My truck also has an electric motor running when I key on. It is from the engine compartment and not the fuel pump down on the frame rail under the cab. I believe it is the vacuum pump. A common leak in the vaccum system would be the cruddy 4wd air lines which would leak down while the truck sets and cause the pump to turn on at key on.

Unplug the vacuum pump and see if the noise goes away. Only side effect is lack of auto 4wd and the HVAC will default to defrost. Plug back in when you're done.

If you have an air leak between the fuel pump and the engine, you would see fuel coming out since the fuel is pressurized under the hood.

[melmount]

I thought the same on the fuel only leaking out. I tightened the water in fuel sensor torx screws and It makes the noise more often now. I have 2 O rings coming from Replacement O-rings for Diesel Engines
I am going to see if thats it. I will post as soon as installed.
The vacuume lines, how does the vacuume get to the front hubs, to and from where? I see two places off the hub brackets towards front of the truck? Mine has some sort of plug on it. I tried to trace any lines, but i see nothing going to my front end?
I willmanually lock them.

[Highbeam]

The OEM vacuum lines ran from a push on barb fitting right on the hub up to the frame rail attached to the brake line and the ABS line. Each hub would have three different lines running out there.

Up under the hood behind the p-side battery is the vacuum pump, the reservoir, and the control solenoids. Unplug the electrical supply to the vacuum pump and see what happens.