Low fuel pressure - Regulator bad?

[michaelsellars]

Hello,

I only have 19psi of fuel pressure on a '73 280sel 4.5 (Should be 30psi). When I turn the adjustment bolt on the fuel regulator there is no change in pressure. The service manual says this means the regulator is bad. Is this correct? Also, isn't it possible that the pump is weak and/or the filter needs to be replaced? Thanks -Mike

[michaelsellars]

I also should have asked: If I have low fuel pressure can that be the cause of 4 cylinders missing or is that a seperate problem? Thanks -Mike