hi everyone i had a very bad day yesterday after loading my families atvs on our trailer and heading 40 miles away the 6.0 let me down. the check engine light was on about a month ago but the truck was running perfectly so i unhooked the batteries and reset it and the cel had not been back on until the start of our journey yesterday. the cel came on and the turbo barked and then every time i hit the throttle i had no boost till about 2500 rpm then the boost would go up to 30-33 psi only going 60 mph. so after making it to the trails and making it home i took it to advanced auto to read the cel codes and they pulled the po299 underboost code. now i know that this has been brought up many times but i cant find any where the truck has been over boosting like mine was. and also i did check all the boots and they all seem to be fine.
i really don't want to take it to ford until i know some of the cause because the truck isn't under warranty

also only mods to the truck are mbrp 4 inch turbo back exhaust and afe stage 2 cai

 

You need something to watch live data from the pcm. You need to watch vgt and see what is going on. Check the map sensor hose for cracks and make sure the nipple on the intake is clear, push some weed eater line through it. Do the same for the ebp sensor, clean the tube and make sure it is clear. Last clean the turbo veins. Live data will help narrow down what is going oon.

 

My money is on a sticking turbo. Been down that road too many times. That's why Ford finally did a buy back on it.

 

FWIW, I cleaned out the EGR, EBP and MAP tube. No change.

I am not as far along as you, other than a cold start problem, truck runs normally. I am looking at the Garrett Powermax from Sinister. $1089 then it is just labor to install.

Thought I remembered the Ford remanufactered units were about twice that.

 

There's another direct swap a/m turbo that doesn't need a tuner. Just can't think of the name right now. I'm sure someone will chime in with a better memory and maybe some experience with it.

 

polish it up and clean it. Thats my bet

 

Depending on where the vanes stick open will help determine the psi. Mine too ran with more psi but pulled a P0299 underboost too.
Once determined it was a stuck unison ring and fixed, I had less immediate raw power but instead, a more consistent pull.
Just because your turbo spools up over 26 psi doesn't necessarily mean it an overboost condition code.

 

Cleaning the turbo vanes and ring is fairly easy, the worst part is taking the turbo off. I too had the P0299 code, I think the main fix was cleaning the EBP and tube.