A clogged Air Filter can also cause the low power symptoms.

In order to check if the ADLA is getting Pressure you need to T into the line between the ADLA and the Switchover Valve and hook on a pressure gauge that has at least 12-15 psi.

When there is no pressure or not sufficient pressure in the ADLA lines the ADLA will not allow more fuel. That means if the metal Diaphragms in the ADLA are cracked the ADLA will not hold the pressure that would allow more fuel.

While it is nice to know that the hose connections on the Switchover Valve are OK that cannot tell you if the Switchover Valve is plugged with gunk.

Disconnect the hose on the ADLA side of the Switchover Valve and connect another hose to it so you can blow through it. If you cannot blow through the Valve it is likely Plugged. or you could bypass the Switch Over Valve just for a test and connect directly to the ADLA.

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84 300D, 82 Volvo 244Gl Diesel