You check pressures at the upper and lower chamber ports on the fuel distributor. You'll need to buy a CIS pressure tester, or a tester with the correct CIS adapters.

Here is the FSM PDF on it
http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/07.3-1603.pdf

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k