On board Air system?

[lunneborgc]

Today i hooked up my buddies boat to take it back to his house, the truck was running connected the trailer and parked the truck/boat. Got in the truck started it up, and heard what sounds exactly like an on board air system. I know I don't have helper air bags on the rear, but I wasn't aware of any air system like that on the truck, and I've never heard the noise before. Rig's a stock 2006 F-250 Crew Cab Long Bed Lariat. Can anyone explain? Thanks guys - Chris

[ShawnCT450R]

Could have been the vacuum pump for the front hubs. Can't hear it while the truck is running though. Did you mean that you heard it with the key in the ACC position right before you started it? It would only be on a 4x4 also and you didn't state that info so I'm just adding my 2 cents. If you can hear it with the truck running, ????? Here is a bump for ya.

[lunneborgc]

It was after the truck was started, sounded just like a compressor kicking on. Never heard the noise before, it was only on for a couple seconds then shut off. Sounded like it was coming from the passenger side front of the truck. It is a 4x4.

[ShawnCT450R]

Sounds to me like thats what it was then, but I can't imagine that it would be that loud. Maybe your compressor is louder than mine and your engine is quieter, cause my truck sounds like a freight train. hehe The vacuum pump starts when needed and creates the amount of vacuum required to operate the front hubs. It shuts off when the required amount of vacuum is present in the system. Hope this info helps you out.

[lunneborgc]

I'm good with that, thanks for the help - Chris

[GregsSD]

Yes it sounds like the vacuum pump. When you first turn your key on (without starting the engine) you should hear it for a few seconds as it builds up the vacuum.

And both 2wd and 4wd Powerstrokes have a vacuum pump because it also controls the vent/defrost door settings. If your vacuum pump goes bad or you get a vacuum leak then your heater/AC will only blow out the defrost vent.

[ShawnCT450R]

Thats some great info about the vent/defrost door Greg! I didn't know that and I'm glad that you added it to this thread.

[palema]

thanks participation!
good luck!