Quick test is disconnect cigar return line and let it discharge into a 2 litter coke bottle to watch amount of fuel returning while cranking....
If fuel is flowing then lift pump is pumping....

Like the previous post said...there is no diaphragm....just an O-ring around the piston push rod....between the piston and roller assy...

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)