ALDA: How can you tell if it's good for sure???

[87tdwagen]

Hello All:

I just scoured the scrap yards and came up with a spare ALDA from a mid 80's 300SD, with the adjustment screw. I want to replace mt ALDA so as to have the unmolested original tamper proof and all. As far as I can tell my stock ALDA is fine, just wanted to mess with the enrichment now with the intercooler installed.

So I check my original on the car with the vac/pressure pump and get up to 12 psi, holds it. Should be OK, this is my reference. At the scrap yard found same one, tested the same way holds 12psi no issue on the engine. Take it off and compare again.

Now the piston travel in the older unit from the 617 is noticeibly more about 4mm total travel, on my 603 the travel of the piston is only half a mm or so, just enough for it to pop, but no apreciable movement in the piston body. I can't get the piston to move further even using needlenose.

The scrap unit's piston moves freely when pressure or vacumme is applied, the stock one just slightly, both hold pressure fine on or off the engine, Which set-up is correct?? I no longer have a reference

Thanks