The work truck in my signature has developed a problem I (and the mechanics at the shop the company uses) can't solve. Above 10 psi of boost, the gauge needle vibrates rapidly (it becomes a blur about 3 psi wide). This is accompanied by a very faint fluttering/chuffing noise that can only be heard with the windows up and the HVAC system off. Once the wastegate opens at 21 psi, everything smooths out. The needle drops smoothly from any point if the throttle is released. EGT is normal, power does not seem to be affected. I have looked/felt for exhaust leaks and tightened all the boost clamps. The truck has about 75k miles on it, the engine is a 300 HP/860 ft# 3126. The mechanics think nothing's wrong and I'm but the truck never did this until about a month ago. Any ideas you have would be greatly appreciated.

 

First, try eliminating the boost gauge by plugging it off and taking it for a drive. If everything looks good there, I would inspect your Pac Brake. Remove the air inlet hose to the butterfly valve and see if the arm moves freely.

You may not find anything here but its a start. After the ovbious, I would hook the truck up to CAT Electronic Tech and run a snapshot.

 

i showed your post to one of the truck mech's, his responce was if your truck has cruise, during the event turn the cruise off and flip the set resume switches each way for a second or so,this will take a snapshot of a list of perameters that can be looked at later up to four stored events he thought. then pressureize from the turbo inlet and soap it down and look for leaks. check hoses of air pressure system.

norm