Well the pop-off valves that I am familiar with, on the street racer ricer turbos, make a loud, harsh, popping or death-rattle sound. There is no way any Mercedes diesel should be producing that sound from under the hood.

Three thoughts:

1. Check the U-shaped hose that runs from the air cleaner into the turbo inlet. If it has come really loose at the turbo it can make a sound SORT OF like a pop-off (my w116 SD did this once in a while, the turbo had shaft play and the sound I believe was the impeller blades lightly contacting the housing... with the hose properly placed you didn't really hear it, but when the hose came off it was clearly audible).

2. More likely he has a late '84 with the '85 EGR setup and is talking about the venting noise (the howl or sigh, I call it) that produces when you go on and off the pedal. (Well mine does, anyway.) Very similar to the sound made by some large diesel rigs in upshifts.

3. Serious leak in wastegate hose?

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22