hey I had a problem like that once. It drove me nuts , turned out to be a bubble in a high point of a line. Each time I would use the hand primer ,it would clear the bubble in the IP. I resolved the problem by forcing diesel fuel back from the filter connections to the fuel tank ,thus forcing any bubbles out of the line .

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'83 240D 264k on 100% biodiesel/ 31mpg
83 300D 217K the $800 gem
'82 300D 267K the new WVO project car finished and driving for free
International tractor B275 on B100
Ford 555 backhoe on B100
Sargent 25 ton Rough Terrain crane on B50