your shutoff valve should be on the end of the injector pump between the IP and the oil filter housing, not on top of the IP. the shutoff valve has one vacuum line coming from it, should be brown with blue stripe, and a small rubber hose connection to the valve. check that small hose as it sometimes gets soft/oil filled and replace if necessary.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP