Turbo Problem?

[swpoffice1]

My 02 350 7.3 has always gotten about 18 MPG, but receintly it seems that it has become slugish, and the MPG has droped to 14-15. When I take off I hear a noise that kinda sounds like a fan noise, and at highway speeds this same noise (plus a drag) comes and goes, some times accompanied by a whistle. Any ideas?
Steve

[WesinTX]

Sound like you fan clutch is locked up. That would drag your milage down for sure.

[alabamafrog]

I would guess at either fan clutch or exhaust back pressure valve. Can you describe it in more detail? One free easy thing you could try is to unplug the electrical connector from the backpressure valve under the turbo and see if that changes anything.

[WesinTX]

You should be able to turn your fan by hand, while the engine is off, if it won't turn you have a bad clutch.

[swpoffice1]

My very first thought was the fan clutch, but a friend of mine told me he thought it was a by pass valve on the turbo. (I don't know what that is) One thing also was when I made a trip from Houston to Lorado last week I was crusing at about 80 and this sound and drag would consistantly go on and off. When it got cooler outside I turned off the air, and it seemed that it almost stopped doing it. (to my suprise) Also most of the time I also hear a very high pitch whistle when it happens.
Thanks for all of your input.

[WesinTX]

The on and off is the fan clutch engaging when it hot and kicking out when it cools off. The a/c creates more heat which would cause the clutch to cycle more. But it should not be cycling going down the highway at 80 unloaded, if it is then either the clutch is going south or you radiator is not doing it's job. Does your coolant level look OK? I doubt very seriosly that your EBPV is cycling like that.