c15 mxs intermittant low boost

My 06 387 with a c15 mxs cat has low boost most of the time. it seems to be fine for the most part for the first minute or two after sitting and idling for a few minutes such as pulling into a scale or sitting at a really long stop light but shortly after it will drop back down to around 32-34 lbs of boost and never really come back out of it till i stop where as i normally see 40+
here is what i have done so far
cat dealer set valves replaced iva pressure sensor, i replaced 3&4 iva actuator (i did have a code for that) replaced fuel pressure regulator in filter head fuel pressure at idle is high 70 and high 90 at 1500 rpm.
and no codes.
anyone have any ideas of what to check or try before i haul it into a dealer.
i do have acces to a otc genisys with heavy duty software but just have not had time to hook it up and a friend of mine is supposed to be getting the snap-on iq at his shoo in the next couple week so if anyone has any ideas on wha parameters to look at on the scanner that may help diagnose the problem let me know.

 

You've already done the soapy water test on your CAC rubber boots , right ?

 

on the agenda for this weekend. but its just wierd how the problem comes and goes but i will definantly check it regardless

 

I just guessing but it sounds like a heat related leak,(the hotter the exhaust temp gets the more it leaks) I would look for a cracked manifold or loose/broken exhaust clamp (on turbos). The 387 has an under hood air cleaner, the turbos should be almost silent when in a hard pull.

 

well i had what started to be a small exhaust leak somewhere around the top turbo over the course of this week it got really bad. turns out it is leaking around the center section of the turbo and exhaust housing. center section was actually loose and moving. clamp wont tighten up and once removed the two machined surfaces dont fit together tight and the exhaust wheel has some damage. ill post a picture of it. truck has 800,000 so maybe its normal wear and tear im not sure but i'd imagine that turbo takes alot of heat.
sorry if my punctuation and grammar kind of suck but im doing this from a tablet and just learning how to use it..
also to add to my symptoms of low boost when climbing mont eagle tn it wouldnt build full boost till i got down to 11 gear but never built over about 38 to 39.

 

yup that will do it!

 

I sure hope so I'll report back tomorrow once I hit the road. Does anyone know if the pyrometer has anything to do with the ecm??? I didnt see anything in the book just glancing through it and I'm thinking of getting a aftermarket the OE seems slow and maybe somewhat inaccurate. The exhaust wheel looks like maybe it was getting to hot since the fins look bent over. And I know its a good thing but I have never seen a temp over maybe 900 degrees according to the gauge. But I have only owned the truck for a year so who knows before that.

 

I can't answer that , but I'll bet Mr. Haney could. PM him , if you can. He's not on here everyday, but does check in.

 

Mine looked just like that when it spit out an exhaust sleeve, killed the top turbo. Now Ive got the same exhaust leak on the top turbo gonna try to change the clamp in the morning.