Ok guys, I really need help. My wife said if the Mercedes is not fixed by the weekend, she is getting an echo.

Car:
1979 300sd

Situation:
Car would not go over 20 mph but starts up right away. Primary fuel filter already changed. Feels like fuel restriction. Thinking, well change the secondary filter and should be fine. Changed the secondary and will no longer start.

What I have done:
"primed" the secondary fuel fiter.
Cranked till dead battery.
Verified fuel is going to the IP assembly.
Verified fuel is not getting to the injectors (cracked one of the lines, tried to start, not a drop comes out)

So it appears that fuel is not getting through the IP pump assembly. I dont think it is bad, because it worked right before changing the fuel filter - unless that is what was making it only go 20 mph.

So I guess my question is, is there a way to prime the injection pump? Is there a vacuum hose I may have accidently unplugged when changing the secondary filter? Or could it possibly be that my issue is the IP pump, and that is what was also causing the 20 mph speeds. Thanks!