Excursion has an Air Leak, I Think...

Guys, Not new to the forum but first time posting. Have gotten a LOT of great ideas and have made a number of upgrades to my 2005 Excursion after reading all the great posts on this site.

Now I'm having an issue that my son and I can't figure out. We completed a Oil and EGR Cooler upgrade using an XDP kit last weekend. Put it all back together and there is a definite loud sound that sounds like air leaking in the engine bay. We've been all over the engine and checked connections. No dice. The leak is louder when you try to drive it and there is definitely low boost. Have a SCT X4. There are no codes and other than the low boost that's causing the truck to be sluggish, all other temps/pressures seem to be in normal range. Getting ready to tar it down again and put it all back together if we can't figure it out.

Appreciate any advice and things to check before I do that.

On a 6.0 the oil cooler and EGR cooler job means the turbo and a lot of the intake plumbing came off, so the leak is almost always one of the joints you touched. A hiss plus low boost points at either the boost side (anything between the turbo outlet and the intake) or the exhaust side ahead of the turbo.

The usual suspects after that job: the turbo up-pipe gaskets and the joints where the up-pipes meet the exhaust manifolds (an exhaust leak there sounds just like an air leak and costs boost), the intake elbow O-ring on top of the engine, the cold side intercooler boots and their clamps, the EGR valve O-rings, and the turbo pedestal bolts if they weren't torqued in sequence.

Quick way to narrow it down: with the engine cold, have someone rev it while you listen with a length of hose held to your ear and walk around those joints. Soot streaks around a joint mean exhaust, oily film around a boot means intake side. A boost leak tester (a cap on the intake side with a gauge and an air fitting) will find an intake side leak in minutes.

Dana