I changed EGR valve & put all new injectors in & now the boost pressure works when cold. When engine is normal temp the boost pressure go down to 0 & up to 25 or higher then back down to 0. Then pickup coughs & misses & put petal to floor & black smoke comes out & quits missing, then boost comes up 25 plus then back down to 0.
Has anyone had this problem? My machanic thinks it could be cold air sensor, but when he checked it the code went off.

 

Not sure what a cold air sensor is...

How many miles on truck and what is it primarily used for? Either stuck turbo vanes or the VGT solenoid is taking a dump. If you have a buddy wit ha 6.0, swap the VGT solenoid on the turbo. If not, take the turbo off and give it a good cleaning anyways, here's the link on how to do it: Diesel Technician Society

 

160,000 miles I use it around the farm/ranch for pulling flatbed & horsetrailer. Haven't had any troubles w/ it until I replaced the injectors. I will try cleaning the turbo. Thanks

 

No problem, let us know if it works for you.