99 F350 7.3L SRW. We have been having some incredibly cold days lately (-20 right now), and I've noticed when taking off, I can hear a "hissing" noise under acceleration. I say hissing because I can't tell if its a vacuum or a pressure leak. Once I let off the accelerator, it goes away and may or may not come back when I hit the accelerator again.
I am trying to figure out if it could be the wastegate relieving or the EBPV sticking. I did stumble across a code on my reading that said the backpressure was abnormal (P0470), but it wasn't enough to set a check engine light.

Anyway to check to see what is going on without dismantling everything?

 

I have a 2002 7.3 that is doing the same thing!

 

Check your intercooler and hoses for leaks.
Do you notice any change in power?

 

There is definitely a change in power...when that noise is heard you can mash the throttle and it goes nowhere...checked for leaks and didn't find any

 

At -20 that's probably normal EBPV operation. The valve will close to provide more work for the engine to warm engine/cab faster. I think outside temps < 45, engine oil < 160?. Does it sound jet engine like at the tail pipe?

May want to post in the 7.3 section

 

With my truck, there is no change in power. I recognize the EBPV staying closed when its warming up, it goes away when I tap the brake. The sound I hear is specifically when accelerating, but I don't think there is a loss in power.

 

The 0470 code indicates an EBP sensor malfunction. This may truly be the EBPV sensor, a plugged or rotted sensor line, possible wiring damage...

I don't believe you'll ever hear the wastegate open on these trucks. Did you retrieve that code from your truck with a scan tool?

For a start, attached is a link to Trey's video on cleaning the EBPV sensor and line.