94' e320 will not start

[JOHN07]

I would like some information on this car. I need to know if my fuel pressure gage will fit this car? I use it on Gm cars, but was not sure if Mercedes use the same style port. Also what is the correct fuel pressure in psi? If I want to check the pf relay, is it located behind the battery? There is a black box next to a computer and a relay behind that. I asume the black box is the fp relay. What is the other relay behind the black box? Is there a way to check the ovp without just changing it? I have read some post that state they can take the ovp fuse out and the car will start. Is this true? I don't want to just start changing out parts until I find the problem. Too expensive.
Thanks JohnT