I had to replace the suction side fuel lines on my 300D this summer, they were leaking and also allowing air to get sucked in. Check all the lines from the standpipe to the fuel lift pump on the side of the IP.

I'd bet you have a combination of clogged filters and leaking lines, so you get only air delivered to the injectors, and no start.

I'd also verify that the shutoff lever is all the way up and not stuck down.....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!