I repeat, there no way missing overflow lines will allow air into the injectors! If air could get "sucked" back in, all the fuel would spray out there instead of out the nozzle.

What will happen if the lines are off is the overflow from the IP will dump down the side of the engine, along with any from the pressure relief valve in the filter housing. The only place the fuel goes with the lines intact is down the return to the tank, air won't bother anything there.

There is quite a bit of "chatter" in the inejction lines, just put your hand on them while the engine is running. There are injection timing devices that use a transducer to convert the pressure pulse expansion of the line into a strobe flash. Very nice, if you can get the right one at a price you can live with. However, there is never enough negative pressure in there to pull air in unless you have a cap nut loose or something.

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!