Suggested you start W/basics ie compression test. Have the ignition system tested on a "scope"? What condition is the "secondary" ignition system in? To diagnose such a problem these items are very important!!
With this type of fuel system the electronics only enhance the basic CIS fuel system. Most cars will run even if the electronics fail. This is why M.B. stayed with CIS when all other car makers went back to complete electronic systems.
MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH