I'm pretty sure it's somewhere in the manual.
I didn't know about pressurizing the injectors either.
Anyway, I was working on a 88 560SEL about a year ago. The car was in real bad shape. I changed the plugs, wires, distributor, rotor and injectors. The car ran perfectly except for a slight hesitation from a dead stop. I knew the problem was fuel related. I checked the whole fuel system, checked for vacuum leaks etc. The car was driving me crazy.
Finally, I decided to ask my friend about it at the local Mercedes dealership. I told him about the problem and about the parts I changed. Without hesitation he asked me if I pressurized the fuel injectors. To make a long story short. He pressurized (opened) them, I installed them and my problem was gone just like that.
I am pretty sure the techs on the forum know about this.
ALL NEW MECHANICAL INJECTORS HAVE TO BE PRESSURIZED (OPENED) AND CHECKED FOR CORRECT OPEN/CLOSE PRESSURE AS WELL AS SPRAY PATTERN.