You've got to test this while driving. I've found I can get very little boost while stationary. I've also noticed that while both of my SD's peak at 9.5 psi, the federal version creats boost at about 500-1000 rpm lower than my California version. I guess that's the difference between the KKK and the Garrett.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Your notion is correct and this is a problem on some engines. He should probably remove the cover and inspect the diaphragm visually. At that point, you can spray some WD-40 down the opening in the valve stem to verify whether it is open or not...Bert