E7 with intermittent boost.

[Curtis78]

11 hours ago, OldRedMack said:

You pressure checked the cac and hoses, but did you pressure check the intake manifold? 

I did apply air pressure to the intake manifold while it is installed on the engine. I couldn't get an accurate reading due to the valves being opened. Have you seen these manifolds leak before?

[Mack Technician]

You can play with (roll with turning tool) engine position to minimize the audible HISS and reduce loss to cylinder. You never attempt to get a leak down reading on the system, you want to charge with regulated live air supply and inspect for traceable leakage from cracks, holes and missing chunks of gasket. If the CMCAC is leaking you can isolate the cooler and perform a leak down check on it, Mack has an allowable loss from (exclusively) the cooler.  

 

I like to check the CMCAC system when I'm taking the rockers off, then the intakes go closed. Typically the injectors will also be out and I stick my ear down the injector holes to also check if the intake valves are seating well with that pressure trying to get past into the cylinders.   

[fjh]

49 minutes ago, Curtis78 said:

I did apply air pressure to the intake manifold while it is installed on the engine. I couldn't get an accurate reading due to the valves being opened. Have you seen these manifolds leak before?

K I could be wrong here  However!  i Kinda see this heading the wrong way here !  The chance of a boost leak that changes form large to small and back again are very slim  The only one that could have produced a variable intermittent boost leak you  have checked the ( air drier )has been by pasted ! Yes The gaskets can blow more often a hose lets go  However!  just a note   if you had turned  the engine a bit with shop air on it   there is a spot in the duration of the cycle that everything is almost closed you would have been able to build pressure on the whole Charge air system manifold and all!     Having said that. While Driving And when the power goes away and your giving it full throttle,  Is there a cloud of black smoke behind you?  THAT would indicate a boost leak!  Can you give a more clear description of what is happening and what your seeing when it happens !With no codes ,this is presenting it self as a condition that the puter thinks is just fine ! A wire shorting to its mating wire  (torque limit) switch or boost sensor  or a bad ECU! all are looking more likley! 

Just my thoughts

Edited November 5, 2019 by fjh

[theakerstwo]

For many years i always pressured the cooler and hoses up to the head.By turning the engine and watching the pressure gauge on the pressure adapter you can get about 20 psi against the valves.However i have never check a later mack engine with these funky cam shafts.