LMM: Boost changes on its own??

[unfinished business]

I am wondering why my boost changes while I am driving down the highway...let me explain LOL.

If I am driving 65 mph on a flat road my boost will go from 3.5 to 6.5-7 psi with no change in throttle or load. Then after about 5 seconds it will drop back to 3-3.5 sometimes into the 2.8 range. With the windows down you can actually hear the turbo spool up when the boost goes up. I do not have the AC on and there is no visibile elevation change.

The truck is not throwing any codes. I am leaning towards this is normal or the VGT could be a bit messed up.

At WOT everything works as it should...i think. I see a max between 28 and 30 psi.

Paul

 

[wilsonck]

wind? since you said there was no elevation changes that you could see..

 

[Dozerboy]

X2 wind or a small grade change. Should be able to get a good idea by logging it.

 

[fast03]

stock tune, race tune, tow tune? Even with a race tune I will not see any boost at all at cruise 65mph unless there is wind or a slight grade. I wonder if it is a tunning issue. I do not have a LMM

 

[sweetdiesel]

Vane posistion maybe

A log will show right away,You fuelin MM3could be changing

 

[sweetdiesel]

could it be a leak?


need more detail.....

 

[DuramaxPowered]

IF the vane position tables have been changed, it is probably when EGR is on then goes off.

 

[LBZrcks]

Mine would do this, but only after I put the dpf back on for a lil bit, almost like it was trying to regen.

Have you made any tunning changes that possibly lead to the issue?

 

[Mike]

Log as Simon suggested and also add torque pid's.

 

[Fat_Robi]

My truck has been doing this as well. I thought it was the tune so I put in a different one and it did the same thing. Today it threw two codes P0410 and P0400. It could be related maybe. I have EGR disabled but no blocker plate installed. Any thoughts?

 

[Fat_Robi]

Anything?

 

[Fat_Robi]

I am going to put in the blocker plate and keep the same tune and see if the boost smooths out and the codes go away.