07 Mack Granite AI 427 boost drop

[ghmallard]

Have 07 Ai 427 that the boost drops off when pulling hard loaded. Boost will be 30+ and fall back to 20-22 then will come back and fall out again. No change in rpm’s just boost psi. Boost Does not drop out when empty even when accelerating hard. No lights or codes coming on when boost drops. Truck has 148,000 original miles 13 speed and 4.17 rears. Any help be appreciated on what might be going on? 

[Joey Mack]

Do you hear the sound of air rushing through a leak ? Im curios about a boost leak that opens when pressure is up. What type of turbo do you have and does it have a waste gate? 

[ghmallard]

We dont hear air rushing thru leak when boost pressures up. It will stay 30 plus boost when empty and never fall. Only falls when pulling hard loaded

[Joey Mack]

With no change in RPM's, does that mean you dont have power loss? Just see it on the gauge? 

[ghmallard]

Correct see it on gauge and can feel and hear boost fall off and come back

[Joey Mack]

Im at a loss, guess im not awake yet. 😉

[ghmallard]

We checked it for boost leaks had none, when boost falls out its a dog. Typically just keep accelerator pushed it comes back for few minutes then falls out again. Just does it when pulling loaded not when empty. 

[Joey Mack]

Is the speedometer acting up ?

[ghmallard]

No went ahead anyways and pulled sensors bell housing , back if tranny and front of motor to check em to rule that out

[fjh]

Here is a bit of an off the wall thing to try ! Bypass your air drier temporarily and see if the issue goes away! I have seen air driers dump boost before! Just sayin!