Testing a FPR (190e)
 

I purchaced a used "tested" FPR for my 93 190e 2.3 from ebay, received it today.

It will not hold vacuum when I apply it with my mityvac, it just pumps up and the needle goes straight back down.

Is this unit defective? I am assuming that when I apply vacuum to it, it will hold.

Correct? Thanks guys!

No that is not a vacuum connection. It is a vent in case of diaphram rupture.

The line that goes to the valve cover/airbox/IAC valve hoses is a vent for the FPR?

http://i52.tinypic.com/149cmzl.jpg

denaliano, on the 124 cars the FPR vent line connects to the bottom of the air cleaner breather hose which attaches to the valve cover. As mentioned if the FPR diaphragm ruptures the vent line directs gas to the valve cover instead of dumping it on top of a hot engine and causing an underhood fire.

It's possible that putting a vacuum on the diaphragm ruined it. Best to verify that the diaphragm is intact before installing a faulty FPR.

How would I verify the diaphram is intact?

Fuel pump regulator
 

Should be very similar to the fuel accumulator vent with no leakage .

gotcha, thanks for the help!