Here's a little story I have to share.

A few weeks ago I broke a chunk out of a valve ( no bigger than a thumb nail ), which I found out there known for it. I replaced the valve and another one that was cracked, all new gaskets on the top end, new exhaust gaskets and valve seals.

Before I had the valve problems the truck was putting out between 8 and 12psi on the gauge, now here is the strange thing, now thats its all back together its putting out between 10 and 18 psi. 18 at hard throtle normal crusing speed it's at 10, downshifts up hill goes to 15. I have been watching the boost gauge as not to let it go over 15 to often, dont need to be picking up parts behind me.

I havent changed any settings for before, everything went back together the same as before just new gaskets so I dont know why its over boosting. No codes either.

Any idea's?

 

Do you have a turbomaster or stock wastegate controller?
What year truck?

Could be a bad MAP sensor if equipped.

 

Stock wastegate. the truck is a 98 2500. If it was a bad MAP wouldn't it show a code? I put it on a dignostic and everything is reading normal.

 

More likely a bad wastegate solenoid not venting vacuum properly,I had to wait for the your answer to know what you were dealing with for sure.

A bad MAP might still be part of it though,you should have defueled from overboost or coded with a P0236 at the levels you were seeing.

Or gauge is junk?