Strange one here, on cold mornings (under 40 F) after driving about 5-7 minutes my truck does something pretty strange. At about 1/4 throttle and around 1500 rmp I hear a strange sucking sound that seems to be coming from under the dash - imediately my power goes in the crapper, and the engine sounds considerably different, it almost thumps. If I push the throttle the sound under the dash stops and the truck comes back to life. But, even though I would like to, I can't run at 1/2-3/4 throttle all the time so as soon as I let off and the rpm goes back to the 1500-2000 range the sound starts again and the power falls. I have noticed that if I pull over and restart the truck - all is well.

Any help would be greatly appreciated. . .

 

EBPV (Exhaust back pressure valve). There is an electrical connector under the turbo, unplug it and your troubles are over. These are known to stick and cause your symptoms. Here's the connector:
https://www.ford-trucks.com/forums/a...1&d=1202847452

Here's what it controls:

https://www.ford-trucks.com/forums/a...tid=2634&stc=1

The EBPV was designed to aid in cold weather warm up's. It blocks the exhaust coming from the turbo....that's the whoooshing sound you hear.
You will not have longer warm up times with it disconnected.

 

Thank you, I will unplug the connector today - right now