I have a 2000 7.3 with 295000 miles. I have a 4" straight pipe DIY intake and a stiffer fpr spring (fuel pressure 65 psi). yesterday I started it up and the motor sounded different almost like it was muffled I started to drive it and it was a little sluggish once I got up to about 30mph it smoothed out and sounded normal. it did the same thing when started it up a few hrs later. any ideas on what that sounds like it could be? Not sure if it helps but 2 weeks ago my in line fuel pump went out pulled it off and bench tested it, and it didn't kick on. I took my air compressor and blew a bunch of black stuff out of it, bench tested it again and she kicked on so I put it back on and been driving ever since (still original in line fuel pump from Ford).

 

sounds like a cloged line it could also be gunk from the tank getting clogged in your tank try flushing your fuel lines and also to be safe check your fuel filter if there clogs in the fuel line there will be some in your fuel filter
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Its your Exhaust Back Pressure Valve.

Not sure why it would be coming on right now, it normally only comes on when the temps are low to help the truck warm up.

It has nothing to do with your fuel issue.