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Hissing sound, slight loss in boost(5psi)

5871 Views 3 Replies 3 Participants Last post by  CajunMick
2011 F250 6.7 with 115k
Recent mods:
EGR Delete/DPF Delete
Intercooler pipe upgrade
S&B cold air
Gearhead Hot Street tune

I have started hearing a hissing, like pressurized air leaking, most noticeable from inside the cabin near the center(probably close to the turbo) . I have also noticed a consistent reduction in psi of about 5. I haven't noticed anything else different about the way it runs, it throws no codes, and I don't smell exhaust nor see any soot from under the hood. No exhaust smell from the cabin either. I also have noticed less wastegate and turbo sound (no surprise there). Can anyone weigh in on what it could be? I have fumbled around near the turbo but can't feel, see or hear any source of the leak, and it's particularly noticeable under load. I haven't figured out how to drive it and have my head near the turbo.

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I dont remember a drop in boost but my hissing sound was a loose back pressure sensor creating a hiss center to pass side, kinda tough to get to but worth a look

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That's what it was, it had come completely off. I forgot to post a response in this forum, but yes, that was the source. Apparently they are notoriously undertorqued, so a good first place to check for anyone hearing that sound. Thank you for the reply, Gummer350.

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