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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? 

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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? 

Had a very similar problem with a 2005 CV713 AI engine. Boost would build up great for a few seconds and then drop back to what felt like 3/4 throttle. Replaced injectors, adjusted valves , replace muffler, pressure tested intake system,  check fan clutch for staying on, check parameters such as tire size and gear ratio in ECM. Engine ECM was at step 10 and VECU was at Step 12B. All looked perfect. Come to find out there are different versions of the Step 12B program and there was a Step 10A  update on the engine ECM that was not visible from the dealership side. Tech support set up a different version of the Step 12 B and an updated engine ECM software. Installed the updates and ran %100 better and held boost at the 30 psi under a load all the time. Hopefully you can find a dealership that will do the updates 

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