OM642 Boost Leaks: The Turbo Resonator That Cracks at 120k

A Sprinter that pulls fine on flat ground and then goes soft on a grade is almost always leaking boost, and on the OM642 the first suspect is the plastic turbo resonator.

The symptom pattern

Why it cracks

The resonator is thin injection-molded plastic mounted in the V of the engine — one of the hottest spots under the hood. Years of heat cycling embrittles it, then boost pressure splits it along a molding seam. It rarely blows open; it opens a hairline crack that only leaks at pressure, which is why it can pass a visual inspection.

Finding it

Pressurize the intake tract at 10 to 15 psi with the engine off and listen. A cracked resonator is loud once the system holds pressure. Spraying soapy water along the seams finds it if the leak is small.

Fix it once

Replace it with a reinforced unit. Putting another factory-spec plastic part in the same location buys you the same failure on the same timeline.