Don't know, How are you testing? Should be isolating booster by attaching vacuum test pump to single hose leading to booster pump. What are you results?

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Mike

82 240D 97K Original (Sweet)
96 Ford F350 CrewCab Dually,7.3 PowerStroke,144K
(a real workhorse, does anything I need)
04 VW Jetta GLS TDI, 33K (50 mpg & it's quick)
Notice a trend? All diesels

63 Chevy II Nova Convertible (wife's) awaiting restoration - Well everyboby has a little gas every once in awhile