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?

 

EBPV all the way. This helps the truck to warm up faster. You'd really see a show with an EBP PID on a scan tool/gauge.

 

If it is below 37 degrees F and your engine oil temp is below 140 it is more than likely the EBPV. When one of those temps rise above the threshold temp you should no longer hear it.

 

As stated, EBPV definitely. You will never hear a wastegate on a 7.3L.

Does the truck feel somewhat under-powered when it is hissing as well?