The original factory style primer pump is notorious for leaking. It is white and mounted on the side of the injection pump. The new type is black and works much better. I t is almost defiantly a fuel supply problem. Why are you using an extra electric fuel pump?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine