After 10mins stopped good boost

[Frank8065]

First of all, thank you for this forum and all the people that keep the info coming,
I have a 2015 t660 isx set @450( or 455),
I have a small issue with the turbo boost, when I take off the 1st time , I go thru all the gears (13spd) and my boost is right at 38 or 39, after the speed gets up there and the boost goes down the next time I get on the throttle the boost wont go past 28-30 psi,even if i downshift, however if i stop for a few minutes , lets say 5-10 mins, while my engine idling I can hear a pssst sound coming from the egr, after that sound i take off amd the boost is up to 38 again only for about 4 or 5 mins ,and the issue keeps repeating everytime I stop for a few mins or go down a long long hill where i am off the acelerator, I already changed the exhaust back pressure , looked at the IMAP sensor and another pressure sensor that sits right by the egr, they where fairly clean, I have warranty on it but im trying to learn this isx stuff, this is my first isx, i have access to insite, there are no codes, really need some ideas here, truck has 150,000 miles on the truck

Thanks a lot, specially to Rawze!!!!!!!!!!!!!!

[Rawze]

(08-21-2016 )Frank8065 Wrote:  First of all, thank you for this forum and all the people that keep the info coming,
I have a 2015 t660 isx set @450( or 455),
I have a small issue with the turbo boost, when I take off the 1st time , I go thru all the gears (13spd) and my boost is right at 38 or 39, after the speed gets up there and the boost goes down the next time I get on the throttle the boost wont go past 28-30 psi,even if i downshift, however if i stop for a few minutes , lets say 5-10 mins, while my engine idling I can hear a pssst sound coming from the egr, after that sound i take off amd the boost is up to 38 again only for about 4 or 5 mins ,and the issue keeps repeating everytime I stop for a few mins or go down a long long hill where i am off the acelerator, I already changed the exhaust back pressure , looked at the IMAP sensor and another pressure sensor that sits right by the egr, they where fairly clean, I have warranty on it but im trying to learn this isx stuff, this is my first isx, i have access to insite, there are no codes, really need some ideas here, truck has 150,000 miles on the truck

Thanks a lot, specially to Rawze!!!!!!!!!!!!!!

(Assuming the engine still has factory programming in it ...)


A 2015 ISX engine is a CM2350. They have a higher compression ratio than older models and only need about 32 lbs of boost or so TO MAKE MORE THAN 625 hp...

From the Factory,... They are well known to over-boost at times up into the 38+ range and it is not so good for that engine.

The real question is ... Is it settling back to normal levels? -- or is it normally over-boosting and yours is jumping into a silent derate?

Those engines have several operating modes in the engine. City, Highway, High altitude, temerature management, etc. so it sounds like the boost levels (or the derate) is changing when it switches from city to highway mode? - or perhaps from "rapid warmup" mode to highway mode? -- Either way, that is what you are doing when you let it sit for 5 - 10 minutes. It reverts back to one of these temporary modes until you get it back up to top gear and going down the road.

I personally think it is perhaps over-boosting in the "warmup" or "city" mode, then settling out to normal levels once it gets up to temp. Most of them i have driven only get to about 32 PSI boost,. and that is where they should be.

============

Little known fact about the CM2250/CM2350 engines ...
Every time you fill up the fuel tank, and do NOT top off the DEF tank too,.. There is a silent 10% power derate that kicks in until you top off the DEF tank again. -- What a crock of horse poop eh?

[Frank8065]

Thanks for the reply,it does have original programming in it, i had never heard of the different modes(city - hwy etc etc), but yes, it only boost 38 for a short period of time normally up to last high gear and thats it, once you down shift it only produces 28-30 psi

[simon999]

I have also 2015 (2014 engine) isx 450hp. Have this truck since new and boost was always 28psi max.

[in2trux]

(08-24-2016 )Frank8065 Wrote:  Thanks for the reply,it does have original programming in it, i had never heard of the different modes(city - hwy etc etc), but yes, it only boost 38 for a short period of time normally up to last high gear and thats it, once you down shift it only produces 28-30 psi

Do you really need to push it that hard or just looking for normal?
We try to keep it under 30 pulling heavy on grade even though it will go 38-40 max.

[Rawze]

(08-25-2016 )in2trux Wrote:  

(08-24-2016 )Frank8065 Wrote:  Thanks for the reply,it does have original programming in it, i had never heard of the different modes(city - hwy etc etc), but yes, it only boost 38 for a short period of time normally up to last high gear and thats it, once you down shift it only produces 28-30 psi

Do you really need to push it that hard or just looking for normal?
We try to keep it under 30 pulling heavy on grade even though it will go 38-40 max.

That is a wise thing to do, but you have a CM871. They are supposed to max out at 38 PSI. A 2350 is only supposed to be 32 max.

Just clarifying for those who don't know