That line from the banjo bolt on the rear of the intake, through the crossover and down to the ALDA needs to pass the pressure from the intake to the ALDA freely.
A way to check it is to pull the line from both the intake, at the banjo bolt, and then pull the line from the ALDA. Just blow through one end. Should blow easily. If it does then eveything there is in good shape, if not start cleaning up the line at the banjo bolt and continue until the blockage is removed.
These get plugged often in these old diesels. Oil, fuel, dirt and whatever pass into the intakes. Just look down yours next time you have the air cleaner off. Not a pretty sight.